At Airsoft World right now is an M67-shaped Gas Charger made by BAW so you don't look like carrying a gas can when you are in the field... "An all metal replica grenade used to fill your magazines or gas grenades in-game without the need to carry a full can of gas around with you.

You fill the grenade with green gas (we don't recommend CO2!) or whatever other gas you are using via a brass fill-valve on the bottom, exactly like you would fill a normal gas mag. Then, when you need to refill a mag or gas grenade on the field, you simply unscrew the fuse block/spoon assembly to reveal a gas plunger nozzle similar to that found on top of your regular tins of gas.

We recommend the use of a fill-valve extender for some magazines as the nozzle may be too short for some models. Also, it's a good idea in colder weather to stick the empty grenade in the freezer for an hour or two before you fill it. This way you will mange to get much more liquid gas into the grenade because the liquid will not expand into a gas as much due to the low temperature. Do not freeze the gas charger in warmer weather -above 20C- or leave it in a hot car as it is likely to blow the seals and possibly permanently damage the grenade."