That I have not found anyone else carrying.
I carry a metal cup. Such as this Cup with a Nalgene bottle in it.
I have found this to be a great carry item. Not only as a cup, but I can use it as a small cook pot, I can use it to boil/filter/collect water, I can use it to signal if need be since it is shiny, I can beat it flat and possible make a blade, also it can be used as the water holder for a solar still. Im sure there are plenty of other uses. I bought a few to put in my kits, bags, vehicles, ect. It is such a cheap and simple item, yet it can come in very handy. It is much better then trying to use tinfoil for boiling, a cup, bowl, ect. If you carry a Nalgene bottle it may be a good idea to put a metal cup on the bottom, especially if you don't carry a mess kit with you <img src="images/graemlins/grin.gif" alt="" />.