I would keep the game pretty simple: even more than other game jams. The player won't be able to see very far, so large, open areas are pretty hard to implement. I'm going to keep most of my sprites 8x8.
Pocket Arcade and Tiny Arcade have a 96x64 screen. You could look at what people have done with it for inspiration. Here is a link to one of my projects Mutant Road. Unfortunately I never got around to making the game more complete.
