created is selling a t-shirt and poster featuring a handy guide of stuff to know and do should you ever get stranded back in time. For instance:
Aluminum used to be more valuable than gold. Depending on when you are, it still is. Extract it from rocks by dissolving them into molten cyrolite and running current through it. You'll find cyrolite in Greenland, latitude 61.2, longitude -48.16. Look for glassy white crystals.
Update: The graphic was made by Ryan North of "Dinosaur Comics," which I also love. (thanks @Skwid!)