A popular container for micros is a magnetic keyholder. Obviously there's not much room inside, but as you can see here, there is a tiny hand-made logbook, a tiny stub of a pencil and a tiny ziploc bag (it's still in the geocache with the white paper in it) to keep the logbook dry. There were actually two tiny trade items in this geocache, which is a bit unusual - there was a shark tooth which is in the cache, and there was a small pin (which is actually in my hand that is holding the cache). The white paper inside the small ziploc bag is a little paper that explains what the geocache is, in case a "muggle" finds it, this way maybe it won't get thrown away if found by accident by a non-geocacher.
We found this one this weekend after apple picking and I took a picture to show you. DH will often look up some geocaches whenever we're going on any kind of a little trip where there might be time for a little geocaching. Makes for fun and interesting side trips! :-)