Words of wisdom:
Pooping and peeing are basic human functions that we all must perform. Bathroom visits are simple in a sticks-and-bricks house with indoor plumbing, but take some extra thought in a camper. Small vehicles may not have room for a full toilet, and those with a toilet aren't going to have a standard flush toilet. Obtaining water and taking care of sewage (“black water”) are both constant concerns when living in a vehicle.
If you don't have room or don't want to deal with sewage, you can stay near places where toilet facilities are available. This might be in paid campsites, a friend's driveway, 24hr stores, fast food joints, rest areas, etc.
Essentially, you have to decide if dealing with your own toilet is more or less of a problem than finding someone else's toilet when you need it.
In order of least to most primitive:
People with vaginas have often used empty 2lb coffee ground tubs in the van, due to the extremely wide opening that makes it almost impossible to miss. For peeing outside the van, they may find a Go Girl or SheWee-type device helpful. Consider this amazon review:
I peed everywhere. That bush? Yep. Peed on it! That tree? Uh huh. Peed on it. Those tiny woodland creatures? Screw you, b*tches! Peed on them. I peed in the sun. I peed in the rain. I peed just for fun. I peed down a drain. I peed in the light. I peed in the dark. I peed left and right. I peed in the park…
The most common poop receptacle for van use is the bucket toilet. At it's simplest, it's a bucket with some kind of liner for easy removal. The deluxe bucket toilet (~$20) has a seat/lid and may also involve sawdust or kitty litter.
Composting toilets don't have to be emptied after each use but cost many hundreds of dollars. See why the bucket is so popular?
Folks without room for a bucket can use doubled grocery or trash bags. Tie off and dispose in trash after use, as one does with baby diapers or dog poop bags. Tip: those doggy poop bags are a good way to store the tied off bags until you can get rid of them.
In the wild, where allowed, one can dig cat holes.