For me it's the music/audio. For whatever reason, making a simple catchy looping game song isn't that hard for me. So I will go the whole game knowing I need to make a song, and on the last day I'll spend 20 minutes to an hour busting out a little song or two and throw it in. Listening to some of these back years later I'm always impressed that they are as good as they are. haha They aren't masterpieces, but for the amount of effort I put in, they surprise me.

Fun side story, one game jam a few years back, after making the music and having less than an hour left I really felt like we needed some sound effects. The game was dealing with building robots and things, so I ran out to my garage with my phone and recorded me using a bunch of different power tools and stuff in different ways, and threw them into the game. They ended up fitting perfectly into what we had made.

Last minute additions to games can be risky, but sometimes they are the best decisions and can really add a lot.