In addition to the very,very basics of w/t/c, stops and turns, I'd say it would serve any trail rider well to know how to ask for and get sideways and at least turns on the forehand (yield hq). You never know what you're going to encounter on the trail and what you'll need to be able to do to get yourself and your horse safely out of ,around, or thru it !
The first time we needed to turn around on a narrow trail,I forget what was blocking forward movement, with a few horses stopped in front of us,, I swear I could feel Sonny thinking "so this is the purpose of it" when I had him do a hq yield x 180 degrees to get us headed back up the trail. Other folks had to do a regular turn with forward motion and got all off into the heavy bushes, etc. on the sides, while we managed to turn around without getting off the path.
Sideways comes in very handy when you run into gates that aren't on the map, or weren't supposed to be closed when you got to them. Speaking of maps and markings on the trails...never ,never good ime.
Yes, YES to the one rein stop and having practiced it ad nauseum in a calm situation before ever needing it, having been taught in a lesson situation how to s l o w l y ask for it.
Although a lot of instructors , esp. if geared toward showing/arena only..don't include helpful trail lessons,,there are options available. One of our local natural horsemanship trainers has an annual one day clinic geared esp. for trail riders/horses,and he also has an annual trail obstacle day.
If you're an ACTHA or the other obstacle trail group (sorry , I've forgotten the name) member, then you have lots of opportunities to help your horse get confident with suddenly coming upon people and strange man made obstacles on the trail.
A good trail horse is worth his weight in gold, imho.