This will teach you all you need to know on the non-supernatural realm, as well as guaranteeing you a spot as the greatest person in history. (That is, if you are prepared for the soul-crushing horror when you return to your own time and realize that you have changed history, and that everything and everyone that you knew is no more. But on the bright side, you’ll be really famous.) But if you are being attacked by Lovecraftian horrors from beyond time and space, then what you really need is this t-shirt for inspiration and a gun to back you up.
This shirt, along with a limitless supply of ammo, will probably do you fine. Note: do not try the same trick if you have not travelled back in time and are just lost in a foreign nation and you think it looks kind of backwards. They probably have AK-47s, and they will kill you.