You can use any fruit you want. Make sure it's washed and clean and cutt off any tough skin and cut it into sensibly sized pieces.
Highly recommended - strawberries, pineapple (fresh, canned would be too soft), mango, apple, pear, grapes, bananas,
Other sweet treats - marshmellows, biscuits, bread, breadsticks, mini donuts, sweet biscuits, profiteroles, strips of cooked pastry, shortbread, gingerbread men, fudge, sweets
You can of course use other delicious items that you like. Things should be able to withstand some handling and dipping, and you want things people can bite or eat in one go so you're not having things licked and dipped back into the fountain.