I want some sort of cold/rain shelter that can fit in a cargo pocket or better yet a back pocket. There is too much of a possibility of me being forced outside without having time to grab my coat or BOB.

So far I have tried plastic ponchos and tube tents. They seem to work well enough to provide temporary shelter. I would like something a little bit warmer or sturdier.

For warmer in that size constraint you might try the aluminized mylar bivy bags.

For sturdier in that size constraint you might try contractor grade garbage bags.

If you can carry something larger I would suggest getting a sil-poncho from ID. It will only weigh around 10 oz but it will be bulkier than a back pants pocket. Might fit a cargo pocket but it would be noticeable in bulk. I carry a sil-nylon tarp in the back pocket of my vest but that is a full game pocket covering the entire back so when I fold the tarp flat it covers my entire back and doesn't form a lump.

I have a fair bit of experience of sleeping under a coat <img src="images/graemlins/grin.gif" alt="" />. You can actually stay quite warm like this. I did it by having my feet in my rucksack and the coat covering me. Not exactly luxury but you can get a relitively good nights sleep. It doesn't protect you from the rain though. You can use the lightweight polyester (or whatever) poncho. This is the combination that I carry.

There is nothing better than sticking your feet in a cosy rucksack!
It really does make a difference. But I have never slept well when I am cold.