El-Cheapo:
The black plastic Kodak film canisters for the advantix film work very well. They need to be squeezed just a bit to fit two cells in them. Free for the asking at your local photo shop.
Raid the kitchen:
Use the little plastic rubbermaid containers for food, and leftovers. Cheap and pretty indestructible. Can also fit spare bulbs, o-ring lube, etc...
OK Spend a buck:
The orange match containers in the camping section at wal-mart. (not my original idea)
Spend lots of money:
SF SC1, SC2, SC3.
Live Very Dangerously:
Toss open cells in pocket with keys, change, etc...
Minimize carrying spares:
Leave a stash at work, in the car/truck/boat, at home, etc...