What are some must have android apps?

Angry Birds ?

Do you have MIUI?

If so, Notch notifications

TerraGenesis, it's a nice terraformation simulation.

Any app that allows you to instantly use your Camera's flash as a light source.
Best when Android adds this feature to the lock screen by default (Older versions didn't)

Free apps:
PGAF
9gag
Radiogram
SoundHound
Windy.com - Wind, Waves and Hurricanes Forecast
Sky Map
Tiny Scanner
Cx File Explorer
QR Code Reader

Paid apps:
Weather App Pro
Weather Radar Pro
Ex Music MP3 player pro - (7,99€) FREE right now

Beat da Beat https://play.google.com/store/apps/details?id=com.nekki2players.beatdabeat
Catan Classic https://play.google.com/store/apps/details?id=com.exozet.android.catan
Hungry Shark https://play.google.com/store/apps/details?id=com.ubisoft.hungrysharkworld
Lets Create! Pittery https://play.google.com/store/apps/details?id=pl.idreams.pottery
Shadow Fight 3 https://play.google.com/store/apps/details?id=com.nekki.shadowfight3

You might want to install a QR & barcode scanner. I always install Nova Launcher (custom launcher which is usually superior to the factory ones, you may choose another one), Textra SMS (custom SMS app, if you actually send/receive SMS messages) and Alarmy (a great customizable alarm).

Other apps I always install are 2FA apps (especially Google's), my VPN service's app, eBanking apps for my bank accounts, Office Lens which is superior in scanning documents, Offline survival manual and Vivino because I keep forgetting which wines I've tasted and whether I liked them. :)

Apps

Steam - Mainly for auth
Steamgifts - So you can leech while you're not at home! The application is no longer supported/developed but it still works. Get APK if you don't want to install F-Droid.

Bluemail - My favorite e-mail application for android. It lets you manage unlimited amount of e-mail accounts on it for free.

F-Stop Gallery - Best gallery application I could find after QuickPic went to shit. Has decent amount of features and lets you hide/exclude folders from the gallery.
Fleksy Keyboard - My favorite keyboard application. Has useful gestures and some nice features, I recommend giving it a try.
Nova Launcher - I'm not going to go into detail about what android launchers are, so I'll just recommend giving it a try and messing around with it for a bit. I like it so much I bought the premium version.
X-plore File Manager - My favorite file manager, I love the dual-pane system and the overall design. You can password-protect it.

Those are my must-haves. Other appliations worth mentioning that I use: CameraMX, MX Player, Droid Info / My Device, Cube ACR (call recorder), AppSales (shows you apps/games on sale and premium apps/games that are currently available for free)

Games

Soul Knight - A fantastic action dungeon-crawling roguelike shooter with good amount of classes and tons of weapons (both ranged and melee). I've been playing it for years and I still can't get bored of it. It's still being updated too!
Hoplite - Turn based strategy puzzle roguelike. You'll need to pay to unlock all levels but it's cheap and very worth it if you're into this kind of games.
Blades of Brim - The only runner game I enjoy. It's not being developed anymore but it's really fun. I can't believe this didn't get more popular, I've been enjoying it for years.
Hex FRVR - Nice, simple hexagonal block matching puzzle game.
Cardinal Quest 2 - Decent roguelike, everything can be unlock for free.

I HATE the vanilla launcher, so something like "Evie" is a good start. (I know others have recommended Nova - but on my budget phone that runs crazy slow.)
Then "Should I Answer" to autoblock spam calls.
A good file manager too, I use "Astro".
You need a QR/Barcode reader, "Binary Eye" is very fast and tiny.

If you want a game, I recommend "Triple Town", I love it.

Evie
Should I Answer
Astro
Binary Eye
Triple Town

Right now I am primarily using my Android tablet as a navigation device. My previous software is no longer supported, but Google Maps works just fine.

Spotify for music
and I think there's a free very cool football game named Dream Soccer and you can easily find some cool free quizz games (there's also way too many free RPG etc. you can easily find what you want)

You could try Chrome Remote Desktop if u need fast and comfy way to work with ur remote computer.
I recommend use Sololearn if u need to quickly learn basis of many programming languages.
I play Raid: Shadow Legends much more than other games so u could find it interesting too.

Honestly, for me, Launcher 10: https://play.google.com/store/apps/details?id=com.nfwebdev.launcher10
Putting uniform-sized little icons on a desktop may be something Apple people find the pinnacle of innovation—assuming you are living in 1992, that is—but for me, nothing beats custom-sized live tiles on a mobile device.

If you listen to your own music, I'd also say AIMP: https://play.google.com/store/apps/details?id=com.aimp.player
Better than the desktop version. The only free music player on Android that natively supports FLAC without any distortion. Pretty decent playlist editor. No unnecessary bullshit built in.
If you have some crazy data plan, then you can just use Spotify or Google Play Music, or if you don't mind paying, then Tidal (probably the best of the lot if you know what you want to listen to) or Deezer.

aww this is a hard question since I think I use many apps that maybe are available only for Italy..?
anyways I've always had Samsung phones, I had an old Nokia before but then I switched to the smartphone just two years ago I think, I spent around 100€ for my phone, thieves stole it among other things so I bought another Samsung phone so I'm in the Android field and I don't know anything about Apple..

I use Ajax which is a Ukrainian app linked to my house security/alarm system so I can see everything through it.. very cheap and useful!
then I've got CCleaner, I paid for the full version on the old phone and I managed to have it restored on the new one, it's amazing for cleaning everything up!
I've got the Dispensa Emilia app but this is for Northern Italy only since there are no stores south of Florence ahah it's a small chain opened by some young guys of my region and you can order food (tigelle mainly, I just can't explain what they are so.. this goes =P) and pay with credit card, paypal or even at the store and get your food whenever you want! they're really amazing and I'm proud to support them!
then I've got Hungry Cat Picross, my favourite game ever, I play it every single day, it's so awesome!
I've got the FIS app that is related to the alpine skiing results and such, so I use it only in the winter =P
then there's Friendz, another Italian/Swiss Italian startup that is something like a photo social network that rewards you with points you can spend on Amazon and such, I think there are also Spanish and English versions of it!
I've got then Live Quiz, which is developed by Bending Spoons here but there are similar quizzes everywhere.. every day 2 quizs with a range of 40000-60000 players and every day there are 400€ to share, I won along with my girlfriend more than 300€ with this app =P always through Amazon credit though since they can't sent direct money, but there are no taxes!
Maps is fundamental since I travel a lot, really a lot, so I have downloaded every European map on my sd card =P
PackKing is a nice app that I use to organize my backpack during my short trips!
Picsart is sweet and useful to modify some pics, mainly for Friendz as I wrote above, you can add texts, collages, many things.. =P
Quizup is another awesome app in English, so funny!
Quora is my daily basis of knowledge and I try to write something there too, always in English though since Italian Quora.. sucks =P
I've then got two radio apps - radio24 and radio sportiva - but they're only Italian of course
there's Shazam to recognize songs, then Shopping List which is my real base for what concerns shopping and everything, without it I'd have to rely on yellow post-its and leaflets like I did until 2-3 years ago ahah! it's so great to have a shopping list there!
Songpop is an awesome music game, I play it every day too!
Sofascore is fundamental to follow all my favourite and local soccer teams and more =)
Too good to go is another AWESOME app that manages not to waste any food - it works in Northern Italy but I don't know about other regions, in Sicily for instance there are no vendors or supermarkets that use it.. through it you can buy "mystery boxes" of food that is gonna expire soon at a super reduced price, like 2-3€.. it's great!
Stop! I've got youtube and a google pdf viewer =P

Plague Inc for those times when you have nothing to do :)

Art of War 3 (true RTS on mobile)
Identity V (kid friendly dead by daylight with insane amounts of rocket chair camping)
PUBG Mobile (possibly best battle royale on mobile)
Asphalt 9
Need for Speed No Limit
Dead Ahead Zombie Warfare
Dead Trigger
Dead Trigger 2
Unkilled
Shadowgun
Shadowgun Legends
Jetpack Joyride
Streets of Rage
Streets of Rage 2
Sonic
Sonic 2
Golden Axe
The Walking Dead Road to Survival
Eswat
Tacticool
Bombastic Brothers
Power Rangers Legacy Wars (currently best fighting game on mobile)
Rules of Survival
Sonic CD
The Revenge of Shinobi
Mercs of Boom (XCOM on mobile, even if Enemy Unkown is on mobile already)
Sift Heads Reborn (compilation of the best Sift Heads games on mobile with slight changes, i however recommend the pc versions first or later atleast)
Tekken Mobile (Shut Down)
Star Wars Force Arena (Shut Down)
GTA Liberty City Stories (formerly PSP & PS2 exclusive)
Vainglory (best MOBA on mobile)
Dead By Daylight Mobile (coming soon)
Snipers VS Thieves (its shit now, dont bother)
Into the Dead 2
(maybe) Command and Conquer Rivals (if you want the ''best'' clash royale on mobile)
Sega Heroes (if you want a match game but with Sega characters)
Havent tried Raid or Stained Act 1 yet so cant say yes or no to them
Theres more but i dont remember them.

There are no 'must have' apps. But I always recommend Final Fantasy Brave Exvius.

No Root Firewall
It fakes a VPN connection (which unfortunately means you can't use it and a VPN at the same time) and gives you control over what apps have access to wifi or mobile data connections.

Stardew Valley mostly and Quora if I'm in the mood for some light reading (people ask questions, or for experiences, people answer).

Stardew runs surprisingly well on my phone (S7).

Also going to keep an eye on this thread haha I just got my phone too and I'm not used to actually being able to have more than 1-2 apps or a game lol

+1 Steam, SteamGifts (I think it's still available via F-Droid, but no longer updated).
DiskUsage -- good drive usage overview in a tree view
I like Google Keep for notes.
Discord?
Keepass2Android, if you use KeePass

A good file manager.