I often need a toilet at job sites, where there are none or they are inoperable.
I hate outhouses.
Sometimes there is a suitable spot to dig a hole in the ground and make a little latrine. Usually this is not the most practical route .
My method is dead simple. I use a 5 gallon bucket. A separate bucket or ice cream pail, contains more dry soil to be used as top dressing. The bucket starts off with about four inches of dry soil in the bottom. After each use, some dry soil is placed on top. I never pee in the bucket. A yogurt container or other suitable vessel is used for pee. The pee is dumped outside. Materials in the bucket dry up, just like with cat litter.
One of those foam pipe insulators can be placed around the rim. A very rudimentary seat. I never use a lid. This would impede drying.
These buckets never start to stink. I generally place them in the sunniest, hidden location, that won't be rained on. This allows materials to dry up.
I've been using this method for over 20 years and have never completely filled a bucket. More often, there are only a few deposits. I don't recall ever having an unfortunate incident with this sort of system.
This method doesn't involve the horrible stench or visual shock that would be encountered in one of those rented porta potties. It's highly portable and doesn't cost anything.
I sometimes bring the buckets, loaded with dry soil and ready for use. More often, I arrive with them empty and simply go to the flower bed under the bay window, or other spot that is likely to have very dry soil.
On a few occasions, I have used sawdust, sawdust mixed with soil and sawdust mixed with wood ash.
I have also used this method in the confines of a livable vehicle. Even there, smell has not been an issue. If a spill were to occur, it would require relatively dry materials to be gathered up again.
Loaded buckets are disposed of at the farm or at another suitable location.