I forgot to say that when I was on my mountain climbing/bog hopping walk I did three stand up wees, man stylee! I used my cardboard willies: http://www.pmate.co.uk/ Although they are absolutely fabulous, I didn't like the idea of throwing them away on a mountain side in the beautiful countryside. I know they are made of cardboard, therefore bio-degradable, but they are bright green and really conspicuous.
So I bought a SheWee instead: http://www.shewee.com/ which is made of plastic and re-usable. It's so cool and so easy to use. I shall never worry about being caught out again. It can also be used for nasty public toilets, collecting urine samples and peeing out of the window on trains!
I would recommend the cardboard P-Mate if you'd like to keep one in your handbag or glove box for emergencies as they fold flat. The plastic SheWee is best if you're going to use it a lot. It's very small and discreet and fits into a plastic bag in your pocket.
Now we can all wee up against a wall on the way home from the pub!!!