If it's the silver stuff, aluminum foil works just fine (use SuperScale Metal Foil Adhesive) or Bare Metal foil, although I just never have gotten the hang of using BM foil. It always tears when I try to work with it.
If it's the gold stuff, head to your local candy store and scope out the candy bar aisle for those big bars of Cadbury chocolate. (The chocolate is pretty tasty, too, although it tastes better in Europe. They don't have the preservatives in it that we have over here in the U.S.) Again, you can stick it on with Metal Foil Adhesive. Rubber cement works, too.
For a slightly redder shade of gold (and while you're still in the candy section) check out those caramel-filled Rollo candy drops that come in a roll. The piece of foil you get isn't as big as the Cadbury ones, but when doing satellites, you usually don't need an acre of foil.
Check out a sporting good store or an outdoors shop for those thin mylar "emergency blankets." They're usually kind of a reddish gold color. They're also huge; you could probably model every satellite that's ever been launched and then some with a single blanket.
Bare Metal Foil makes gold foil, too.