Jetpacks make me happy - thank goodness they are easy to make. All you need:
2 oatmeal containers
(or 2 ltr. bottles, or Pringles cans, etc)
2 plastic or styrofoam cups
red or orange crepe paper or ribbon
scotch tape (to hold down stray pieces of tin foil)
I sat down and just pieced together everything; wrapping the oatmeal containers in tin foil and taping it down. Using duct tape to make straps (just tear off a long piece and fold it in half - nice, sturdy strap). I didn't really measure much, but a jet pack is for fun... and for feeling happy. Seriously, make one and try it on, you'll see what I mean. Better yet, walk around your workplace wearing it - the smiles and laughter will do everyone good.