In reply to thin bob:
Ive never had a dump without having a whiz at the same time so dont forget to aim well!!
Being a carp angler, shitting in my bivvy is something ive got down to a fine art and find a mk1 plastic bag, sometimes with a handful of soil (for the piss to soak into) does the job just fine!!
And remember, what you brought with you must be taken away
Enjoy!!