I will put a vote in for the tarp, you can wrap your self up in it like a bivi. You can stake it up as a wind wall/block or a fire reflector/windscreen also it can be draped over you so you can stay "shelterd" while on the move. Tarps are cheep(to the best of my knolage, if the poo really hits the fan you can fit two people in one tarp (preferably, one man one woman) and you can set it up above you for rain and/or sun protection.

And thats all I have to say about that.