I use doggie cleanup bags (about 5"x8") because they're (1) opaque so I don't have to look at my work and (2) mildly scented so I'm not reminded of what I'm carrying on a hot day. <img src="/forums/images/graemlins/frown.gif" alt="" /> And then that's double bagged in a regular ziplock. The bags never go inside my pack. I only use packs with open outside pockets, usually mesh.

If I'm having a campfire, which is rare, I burn it.

There are also alternatives to T.P. which have been discussed here.
_________________________
If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.