The stuff people put in geocaches. Trinkets that have little to no intrinsic value but are traded out by geocachers when they find a cache. The sport of geocaching often includes finding a cache of geojunk and tradition says that you take an item and leave an item. Those items are, more often than not, geojunk. Typical items are keyrings, wooden nickels, etc.
"Are you ready to go geocaching?" "I'll be right with you as soon as I grab my bag of geojunk".