The rule is simple- if you take something, leave something. Sadly new cachers tend to forget this and start feeling guilty. I’ve actually found money, paper money, in a cache along with Happy Meal toys, and other Dollar Store trinkets- my guess is someone was caching with a kid who really, really, really, wanted the rub on tattoo in the cache, so whoever was caching with the kid, bought it.
Besides shiny things and junk, there are those who create intricate signature items. I once thought about buying a bunch of Professor Zoom cards from the DC collectible card game to place in caches… until I found out that “collectible” means expensive. Cecil once put toy parachuting monkeys in caches. He soon discovered pathtags and since they are shiny, and they are collectible… he went with those. They also really confuse anyone the first time they encounter them, because they think they are a geocoin and therefore trackable (more on that Monday). If you ever run into one in the wild, don’t panic, if you like it- keep it.
One big no-no for trading would be food items or something smelly. Items like that tend to attract animals who can either steal or destroy the cache as they hunt for dinner.