Not necessarily. For beans, soak them overnight, come morning replace the water with boiling water (you can use the soak water), then stick the beans/hot water in some sort of insulated wrapping. They'll be ready to eat later that day.

Rice works the same way but you don't need to soak it the night before.

If you are secure in your location and the sun cooperats you can use a solar cooker. A simple one can be made from a cheap styrofoam cooler, a sheet of glass or plexiglass, and a pot painted black.

-Blast