If you're planning on time traveling, get one!

This is a handy cheat sheet for many modern inventions if you happen to travel back in time, although I suppose it would be useful too if civilization collapses around you and you happen to survive.

It is apparently available as a poster or t-shirt, but if you really wanted to make sure you had it with you, why not get it tattooed on?

Brilliant!

I would trade my worthless gold in for cats, wouldn't you? Cats for gold