I'd keep it simple, real simple. I'm thinking like rpg-style here, so I'm not counting keys or anything like that, but if my house keys got me into any door I wanted, then that's sweet.

Backpack full of:
Non-perishable food
Pencils
Paper
Money
Baseball bat
Phone

More or less shit I have with me every day or in my room. I figure I'll start with the bat and make my way up the weapons chain, GTA style baby. Maybe some clothes too, but I dunno.