I nicked this idea off Pinterest. I don't know where it came from, because the link from Pinterest was to someone else who said she found the idea on Pinterest! And I LOVE Pinterest! If you don't "do" Pinterest... well, what's wrong with you!? No seriously, you'll love it too, and probably spend an inordinate amount of time browsing through all the fabulous ideas you can glean from the collective "oh that's cool" findings from around the world. I have ferreted away a plethora of good ideas for how to entertain my soon-to-be four-year-old: educational, just for fun, seasonal artsy-crafty projects, rainy day projects and more.
Among these, The Jet Pack! Two empty Coke 2-liter bottles (or any matching-shaped pair) painted silver (I just used a couple coats of a silver acrylic I had on hand, the version I saw was spray-painted), some ribbon for the straps (or you could maybe use lengths of duct tape, folded over on itself so the sticky part is internal), some craft felt for the flames (the idea I saw used crepe paper or streamer rolls, but I didn't have this, and I imagine Avi would tear the delicate paper fairly quickly zooming around) and hot glue. The idea is to use things you have on hand, so improvise--it's a recycle craft!