Squirrels are omnivores that will even eat pizza. They like field corn (sold in stores as "deer corn", used to bait deer during hunting season), sunflower seeds, and blooms off of a flowering tree. A starving squirrel will even strip bark off tender twigs on any given tree.
They'll eat bread alright. Just be wary about keeping a squirrel coming to your house. If the squirrel fancies your attic to build a nest in, you're going to be looking at thousands of dollars worth of damage and he'll be as hard to get rid of as his mate and kids.
Squirrels are like rats with bushy tails and will eat anything, They do seem to love corn though. I bought some bird seed on sale that has corn in it and now that have been getting into my feeders that they left alone up to now.