I use a micro sd holder that is about the size of a credit card (a bit thicker). It holds 10 micro and 1 sd card (handy for carrying an adapter).
The cards click into slots around the holder. They are held securely. Nothing to unzip or open and very little added bulk.
There's a little hole on the corner so that one could hang them from hooks or chain them together. There are a few different colors.
I like these quite a bit. They're about $10.
http://www.amazon.com/micro-SD-card-...icro+sd+holder