These 'Battery Storage Tubes' from lighthound.com work great for 2x18650, or 4xCR123a.
http://www.lighthound.com/Lighthoun...batteries-or-4-x-CR-123-batteries_p_2803.html
Apparently they are 'pre-inflated' 2-liter pop bottles. Tough, waterproof, dirt cheap. There is just a smidgen of rattle room at the top, so I usually stuff a very tiny amount of plastic-something in there to make it quieter. With no disrespect intended to Countycomm.com, their 'tube vaults' appear to look identical, but are just a little too short (or differently internally tapered) to fit in 4xCR123a cells.
Countycomm does make the only right-sized keychain 1xAA holder I've ever seen, the Delrin 'AA battery locker'.
For single cells, A geocaching 'large bison tube' fits 1xAAA pretty well, and a 'squat' aluminum pill fob is a good size for 1xCR123a.
The waterproof match case mentioned above is fairly size-specific for either 1x18650, or 2xCR123a, except you might want to roll some thin cardboard inside to reduce side-to-side rattle, and perhaps a little wadding on top, but they are not grossly oversized, and they're waterproof, and I think they are about $2 here in the States.