You buy a trowel, a roll of toilet paper, and you walk a little ways into the woods, dig a "cathole" at least 6 inches deep, do your business, put the toilet paper in the hole, and bury it all.
Do make sure you are not digging your cathole within 100 feet of any water source or camp. Don't put rocks over it as this will keep rainwater from getting to it.
Humans have been digging catholes like this for thousands upon thousands of years. It's natural and fertilizes the ground. I hiked the Appalachian Trail in 2016, and unless you are at a shelter with an outhouse, this is how you use the bathroom on the Trail.