I use any of the following, as long as they are cut up small enough for them to eat easily and not choke:   
Baby carrots 
Frozen peas (they LOVE these) 
Cheerios 
Bananas 
Small bits of Cheese 
Whole Wheat Crackers 
Unsalted Rice Cakes 
Peaches (fresh) 
Pieces of leaf lettuce 
Whole Wheat Pasta-they LOVE to slurp up spaghetti noodles!        |