There is no way to cook, prepare or combine food.
Bread should work to use a bedroll (if there are no hostile creatures around, and you have not slept recently), though the game may always check for certain foods first.
I really never paid attention to food; I had enough at the start of the game to use the bedroll, and later I started using the Healing spell more. Eventually Regeneration (based on the Survival stat) was enough to recover between fights most of the time.
