Some of my family members drive truck at farms during harvest and I've rode along a lot. The guy driving the combine can mostly be automated except the part of having to stop and clear out metal or other jams that stop them. The machines have sensors which shut them down instantly when they detect metal because the cutter is expensive as hell. Not sure there's really a way to automate that. There's a lot of other less common things that cause the chopper to stop but foreign debris is the most common.

As far as field trucks go, well they're mostly old 15+ years with new-ish trailers because well trucking doesn't pay shit so it'll be long time before self driving trucks replace the current fleet (you have to figure the new trucks on the road now will because part time field trucks 20 years from now). If can get GPS accurate enough you could automate a lot of it, but trucks get stuck all the time in the field which mean the guy driving the chopper has to stop and pull the truck out.

It'll be tricky to automate all the weird oddities you come across out in the field. In the end these guys aren't making very much so the cost benefit doesn't really seem to be there but we'll see.