I have done this. I have also made French toast from English muffins, bagels, leftover blueberry pancakes (incredibly yummy if done right), muffins sliced into sections, a turkey-burger patty (if it takes the egg coating and fries up on the griddle, it is French toast), leftover mashed potatoes and hash browns (again, if it takes the egg coating), stale donuts, at least 15 different kinds of bread (including Challah, zucchini bread, raisin bread, cranberry bread, sourdough, a baguette, gluten-free and normal white bread, oat bread... you get the idea), Eggo waffles, and slices of cake. If it is bread-like (or even if it is not, in the case of the turkey burger, mashed potatoes, and hash browns), you can make French Toast out of it. All of those taste pretty good with maple syrup or jam.