Less flammable would be Helium. It just so happens that the US is looking to sell the strategic helium reserve. So you just need to find a VC and you can get your backpacker's assistant idea off the ground. hehe

as far as helium balloon, it would have to be a balloon of such enormous size to be of any benefit. To launch a couple pounds of payload to 90k feet required a balloon 8' in diameter on the ground.

A kilogram of lift per cubic meter of helium. At sea level; if you let it expand it only goes bigger at altitude, without needing more helium.

Great, so if I have a 25kg sack, a 1 meter sphere being trailed above is only going to make it 24kg. Like I originally stated, a few pounds required an 8' diameter balloon, so 2.5m balloon. That's friggin huge. FYI, at 90k' altitude, the balloon expanded to about 40' before reaching it's burst limit allowing for a return of the payload.

Lots of fun on windy days!