in the FAQ it states:
What can I work on before the jam? You are allowed to set up your tools and your game engine. Tools include: palettes, fonts, tracker instruments and code libraries.
so you could make some generic components that could be used in your jam game. like a basic character controller for a platformer and/or top-down game or a dialogue system.
EDIT: sorry, i was mistaken!
these things would fall under core game programming and should not be worked on until the jam starts.