Jet pack. Yea.

There's a fully functional jet pack that flew around indoors with huge crowds...the future is here!

Looks almost fake, doesn't it?

In that short little lap, the pack burned all of its fuel - lifting and keeping that much weight in the air is forceful work, and they did this one with compressed air instead of flames.

The trick to lifting something like this is to send molecules downward at incredible speed. Newton's 3rd Law says that for every action, there's an equal and opposite reaction - in this case, the molecules of fuel that are pushed down out of the pack create an equal force upward on the pack. But the molecules weigh much less than the person + pack combination, so they have to be sent down with FAR more speed.

If only everyone was this excited about MOMENTUM :)

It's a basic momentum problem, and it's relevant for any sort of jet pack or spaceship technology, but not airplanes or helicopters. Particles must be ejected in the opposite direction of where you want to go at a very high speed, and that means you need fuel - but you can only carry so much, or it starts to weigh you down, requiring more fuel to lift.

So jet packs may always be just a fringe technology - we can have replenishable energy (solar, geothermal, hydroelectric), but not replenishable particles.