Bean, that's a great idea! My dd would love those for breakfast.
I second the fruit and cheese ideas. Just make sure that everything's easy to eat and clean up. DD and I went to a friend's yesterday and they had sliced strawberries for the two girls. A great snack but there was strawberry juice everywhere! Stick to apples (peeled if toddlers), bananas, that sort of thing.
If you want to reduce the amount of mess you'll have with banana bread, you could always bake that in mini-muffin tins, too.
I always have some whole-wheat crackers or graham crackers around, too, when we have kids over to play, just in case they don't like what else we're snacking on. They seem like good, safe stand-bys!