I have been thinking that opening a Primal/Paleo food cart here in Portland, where the food cart scene is HUGE, might be a good idea. Getting a food cart started requires minimal capital -- several thou and a dream. These days, I'm much more interested in setting up passive income streams, so someone else can do it; feel free to take the idea and run with it.
Location would be critical (and all the good locations have already been snatched up), and there'd have to be a draw-in somehow for all the tons of vegans around here. Maybe gluten-free baked goods, coconut milk smoothies? Also marketing it as low-carb would draw that whole crowd in, too.