I'm usually geocaching with my six-year-old son. Usually I'll let him pick what we are going to take from the cache. It keeps him interested in the hunt and minimizes the whining.
One time I was writing in the log when I looked over and he was blowing up a toy balloon someone had left. Once he had put his mouth on it, I felt obligated to take it. Ended up leaving a brand-new Swiss Army Knife in its place.
On the one hand, he really liked the balloon. On the other hand, I felt kind of cheated. I guess I could have taken something else as well, but it didn't seem right at the time to take two items and only leave one.
Just keep repeating to yourself: "It's the hunt, not the items. . . It's the hunt, not the items..."