Beach Ball + Sharpie = Your cheapest teaching tool ever!
Cover them in vocab words to study.
Use them to review questions about a book or chapter.
Write activities/stations/tasks and use them to make choices.
The list goes on and on.
Toss them around, and the catcher has to answer the question (or define the vocab or pick that activity, etc.) based on where their right thumb lands.
You can make as many as you need for very little money (especially if you buy a stash at the end of the summer) and they are easy to deflate and store, or brighten up a space if you hang them from the ceiling still inflated.
Per the request of the attendees at my presentation last night- Here are the questions that I used on my Catholic-Get-To-Know-You Ball. Write all these questions on a beach ball, and you have a great ice breaker for your next youth group, Bible study, or adult gathering. (Girls love it because they get to talk about themselves, and boys love it because they get to throw things inside.) The questions are geared more towards teens and adults, but you could certainly adapt them for younger kids.