Can the helium from a gas bottle lift the bottle? Does a gas bottle full of helium contain so much helium that, if the helium can expand into a baloon, can lift the empty gas bottle?
And input on this question highly appreciated...
 A: Typical bottle volume 50 L, pressure 200 atm (values used in scuba diving). This means that the expanded helium would have a volume of 10,000 liters, providing about 10 kg of lift. That is not enough to lift a typical scuba tank (about 15 kg).
So I would say "no", for a long thin tank (shaped like a scuba tank). It would be possible to conceive of a helium tank that could do this. Obviously, a lower pressure tank with larger diameter would have a more favorable ratio of mass to volume: if you say that the wall thickness scales with pressure times diameter (same amount of material supporting same amount of pressure), but the "potential lifting capacity" scales with pressure times diameter squared (expanded volume), then you can see that a larger diameter tank could do it.
Update - I found specifications of a helium "K type" cylinder. They cite a pressure of 2200 psi, volume of 217 cu ft. That translates to 150 atm, 6145 liters (expanded... or 40 liters unexpanded). According to Wikipedia the K type cylinder has a mass of 110 lbs or about 50 kg. It won't fly...
