I have a Snow Peak stove and it works great for what I use it for. When I am in the backcountry I only boil water with it which means that one of those small canisters can last me 5 days if I am careful. However I always take along an unnecessary second canister because I have read of cases where backpackers had problems with the canister not re-sealing when the stove is removed and the gas slowly leaks out and then they are stuck with no fuel. I have NEVER had this happen in dozens of trips, but out of fear I take along the added weight of a second canister. Does anyone know of or use some kind of small screw cap on the canister to make sure no gas escapes after the stove is removed? If I could find something like that I would leave the second canister in truck and enjoy a lighter pack.

I carry the second canister also as a back-up and would love to know if there is a solution.

I think there is some risk when the stove is left on the canister, so I always remove the stove once it's cooled down. There is a small amount of gas that escapes when screwing on/off the stove, but have never lost gas when the stove is removed.

I don't bring a second canister unless I think I'm going to use all my fuel and then I just upsize my canister instead of carrying two.

I carry another small canister as back up as well.

Boiling water for five days for one man with one 8 oz. (actually weighs 13 oz. because empty canister weighs 5 oz.) is pushing it IMHO. I weigh my canisters after use and mark the weight on the bottom of the canister with a magic marker. For five days I would take a half-empty canister and a full canister.

If you don't have a half-empty canister then Chiro's idea of carrying a small canister is not a bad idea.

It really depends on how efficient your stove and pot are, and how aggressively you boil your water. I find that getting water just barely to a boil is plenty to re-hydrate my freeze-dried meals in the advertised time. If you really get your water to a rolling boil each time, then you'll use more fuel. I use an Olicamp XTS pot and a Soto Windmaster stove that I run on low flame until the water just starts to boil, and can get over 30 such boils to an 8 oz can of fuel.

Having said that, I always carry a small backup canister of fuel just because I'm always thinking of the rare case where a canister leaks and leaves a guy with no fuel.

Used those canisters and that stove for years, never had an issue with leaks. That said I carry a single wall cup which I can use to boil water in a fire if need be. I usually have a small fire at night anyway. Often use hardly any fuel. I would never carry a double wall cup or nonstick cup/pot for this reason--you are marrying yourself to your stove which is pretty silly in an emergency situation.

Wow... I have done 10 days on a single small canister. I guess I was only cooking breakfast, coffee, and dinner, and that's with a jetboil.

Like Jordan said though... there are a lot of factors. If you don't have water and are melting snow, all bets are off - that's the only time I've run out of fuel (and the worst time to run out of fuel).