The lightweight dry cleaning bags are best. Most garbage bags are too heavy. Make an "x" of drinking straws & Scotch tape to hold the bottom open & about 5 skinny birthday candles, well clear of the sides. Inflate with hot air from safe source ( mantle lantern or camp stove ) until lifting well, then light sustainer candles and release.
Safety first. No or very light winds. You don't want sterno or other fire source that will light a house on fire. Do Not Use if forest or brush fire hazard exists.
Cheap paper versions are around with the candle included. $5 at local convenience store. Check Dollar stores. You can also buy kits with rice paper ( feather weight) & patterns to make a variety of shapes.
Coworker played that game once. Gassed up a garbage bag . Climbed too quick so he tailed it with a welding rod. Then it just drifted and climbed real slow. I was running bead blaster for several hours so wasn't at normal work station. Got back and Ben was so proud of his bag. Called my attention to it. I looked up, saw it, and where it was. I simply asked, Ben, won't that drag your tail rod right across those 440 volt rails that power the overhead crane? There was a small color loss in his face then and it was on to try to retrieve said bag. I thought it was funny, but he never considered those power bars that sit on top of those beams.
The mass balloon launches at festivals is spectacular. There's a Hot Air Balloon fest in Dansville NY that's quite a good time, with bands and beer sales... They line up the balloons on the ground and fire them up at night for a "Glow".
For those preppers on a budget. And for the rest of us that should have some stores. I like the bean soup option with flavor packs. I'll put some dried peppers at the top for seeds to plant. The beans are seeds.