What's your base code?

So,yeah I'm in again! 5th time! Excited as always!

But let me ask you something I've always wondered about this rule:

You’re free to use any tools or libraries to create your game. You’re free to start with any base-code you may have.

What's your opinion on Base Code? How large is your base code? What libraries do you use? What can or should I put in there? How much is too much?

Thinking a lot about this lately. Haven't used any base code until now. But when I think about it, for example, I always need to code a 2D-Vector/Map to manage tiles, or some procgen code which is always quite similar. Or player input and movement. Or AI code? But maybe some shaders would also be useful? A start screen with a simple menu or scene transition code?

But where should I draw the line? I hope you don't mind asking, but it's something I always wondered...