For exactly that reason, I use a Coghlan's plastic match safe to hold two spare CR123s. There is just room for something like a $20 wrapped around the batteries, and just room in the end for a very thin piece of foam to stop endwise rattle. Plus, it only cost $1.19 at the local store.

http://www.rei.com/online/store/ProductD...gory_rn=4500638
and countycomm.com has what I think is the same thing for $1.00:
http://www.countycomm.com/matchcase.htm .