There is what could be a fun idea. Large container containing a small container containing a ziplock bag. Something to consider though, you will want your containers a fair size for a couple reasons. First, visability. One cache that I read about last night is a film container taped with white tape and containing 2 quarters. OK but how easy is that going to be to spot. Especially if it isn't found before fall when leaves drop. Second consider all that you want to put in your cache. Most contain a log book some information that stays in the cache and the little trinkets that can be traded. Some even include a camera so visitors can photograph themselves. The owner of the cache then replaces the camera and posts the pictures on the web or back into the cache. That could all require a fair sized container.