Van Dwelling/Bathroom

Composting Toilet - there is a compact model made for boats, but a blackwater tank is required for excess urine, which can be emptied at any sani-dump station

Newspaper/garbage bags

The simplest method is to lay out some newspapers. After defecating, wrap it in newspaper, then tie it up in a grocery bag. Dispose of it in the nearest garbage can or dumpster.

Newspaper method #2, wrap in newspaper with sawdust (to absorb moisture) and a handfull of soil, store outside where it can dry up w/o smelling, turns into a humanure compost burrito, yum!

Sawdust toilet

Several plans exist on the internet for making a toilet out of a 5 gallon pail.

Portapotty

Gas station/fast food joints

Good for going to the bathroom, though frequently unclean and smelly

Grocery stores

RV toilet/blackwater system

Cassette toilet

Composting toilet. It may be a little large, but there are [plans for a cheap 55 gallon drum composting toilet].