Large plastic sheets a £1 (morrisons)

[sniper 55]

I noticed Morrisons has 12x9 plastic sheets for £1, they were in the decorating section of my one, I haven't bought one to try as her indoors was in a mad rush to go but next time I'm in there I'll grab a few. They look pretty thin but they might be handy for something.

[gamekeeper752]

keeping in the car for a road kill maybe

[yorkshirewolf]

useful for putting on the bed when you want to cover yourself in oil or vaseline...

[Jamesey1981]

Mors Kochanski's super shelter uses a plastic drop cloth, it's intended for real extreme cold weather, Dave Canterbury also teaches a modified version of it at the pathfinder school.
Both are worth checking out, Mors version is designed for the boreal forest, whereas Dave's version is adapted for the Eastern woodlands which is a climate and environment that's closer to our own, but if you know both then you're better set up to adapt it to wherever you find yourself and you've got that flexibility built into it in your mind.

I would also think that you could rig up a pretty decent rain trap with one too, and there's probably a whole bunch of uses that escape me right this second, like taping them over doors and windows to keep dust out for example.

They are pretty thin, I imagine they'll be something like the B&Q value ones that I bought while I was decorating, they have a bit of stretch so they're not TOO flimsy, but anything you use them for is going to be temporary.