Anything close to the left hand would probably be good - shift, control, E, Q, F (take note of other keyboard layouts tho, french keyboards are in the AZERTY layout for example). You'll probably figure out the proper key easily ^^
And yeah, I know how it is with jam games, stuff like quitting the game is always an afterthought. I think starting with the full loop (game start -> empty level -> end -> reset) is a good idea, this way you don't have to change everything once the gameplay is done, took a few days off of my life trying to figure out how to spawn everything I need after it was all done in multiple games :P