Oh, so like an item, so you can't always jet? That would be REALLY cool, now that I think of it. That would be a pretty cool way of letting particular people get somewhere special, that was built higher than the player can jump. You could do:
Onactivate -> Self -> ifID [-list of trusted ID's-]
Variabletrue -> Player -> Setinvetory -> Jet Pack
Then, they would be able to get to the higher area. GREAT idea.
Quick Edit: There should also be an infinite fuel version. Also, would the fuel regenerate? I think it would be better not to... So you'de have to save it for something particular, instead of jetting around every now and again when it recharges.