Justin Hessler: 2 books

When Sam receives a $100 bill for his tenth birthday, he knows exactly what he wants to buy. But first he wants to share it at Show & Tell at school. None of his friends have ever seen a $100 bill before. But sometime during that day the money disappears. It's up to Sam and his friends to solve the mystery of the missing $100 bill.

Sam, James and the gang are off to 4th grade science camp.  When they arrive, Sam discovers his brand new iPod in his suitcase–which is against rules. He hides it and hopes the camp counselor doesn’t find out he has it.  Later he discovers it's missing.   Now Sam, James and the others have to find it before camp is over or he may never see it again!