Half-life

Give it to a friend.

firts check if have an steam code, i also have an old Blue Shift cd official from Valve and Gearbox and its Non-Steam

redeem it.

when you get the half life complete pack you`ll get a gift copy.

then you can give it away.

keep it for collector's purposes. then, when you're 40 years old and a cranky old shit you can show little kids the game and tell them it was the best game to be released and that your opinion is far superior to them.

hopefully valve will still exist then so that they know you're telling the truth.

if it's Half life only or Half Life Blue shift then you are fine it's a steam key, Opposing force is the only one that you can't register on steam (because if you redem Half-life or Blue Shift you will get the Platinium version with all expansions)

"Opposing Force CD-keys cannot be registered through Steam. Opposing Force was included in a retail Half-Life package. The Half-Life CD-key included in the package will unlock all of the games in that package, including Opposing Force."
https://support.steampowered.com/kb_article.php?ref=7480-wusf-3601
Sorry for no hyperlink