whole grain bread is fine as an occasional treat. Almost any fruit/veggie is ok. However, onions and garlic will make milk taste off.
My goats don't like citrus peels, but my friend's goats devour them. Mine also don't care for tomato at all - not even the plant.
I've given mine peppers, cukes, celery, carrots, apples, pears, pumpkin and squash (both summer and winter), banana peels, lettuce, cabbage, raisins, grapes, berries...