We often feed treats, alfalfa pellets mostly. I always have my fanny pack, like Saddlebag, with treats in it.
I learned the hard way about treating horses. When we first got back into horses, we treated them, but the horses got pushy and nippy so we stopped. Then, I became interested in clicker training and learned why my horses were nippy. I had not been paying attention to their bad manners like ears back and pushing into our space.
When I began clicker training, we built a strong foundation of good manners first. Of our three horses at the time, our food aggressive gelding struggled with it a bit longer than the others, and would revert to aggression occasionally to see if it would work, so I was always VERY firm with him.
Now all of our horses are well trained in gentle treat taking, and we are always ready to go "back to basics" if needed. But that has not been necessary for at least 2 years.
I treat often. When I lead them, I often stop suddenly and treat if they stop quickly with me, or stop and back up, and treat if they stop and back up quickly with me. They never know when I will do that, and I don't always treat them, so they never know.
It also means when they get loose, they are easy to catch. My neighbor came to tell me my horses were loose and was panicked that they were on the road. She was so surprised when I just walked out and called them, and they came at a gallop as soon as they heard/saw me, then calmly followed me back to their pasture. They also come running when I call them in the pasture, even for work.
I feed treats while we ride too. I make a cluck sound when they are doing something really well, like a nice smooth trot with back engaged, or a nice side by side with another horse, and their gates are matching.
I am always looking for a challenge or extraordinary behavior to reward, and I usually find something. I also think it makes them look forward to their work, not just for the treats, but also for the mental challenges.
Yesterday, I treated my mare for going really slowly on a trail while I trimmed branches from her back. She had to listen for each step. My hands were busy, so she needed to listen to my legs and seat only, as I asked her to back up while I pulled a long branch to snap it. She was flawless as she did it, so I clucked as she did. Then, when the branch was broken and placed where I wanted it, I gave her the treat. She was very pleased with herself!
When I treat from the saddle, I tap her with the treat on the side on which I am holding the treat, then she turns her head. I keep her head there for a few seconds, using this as a great neck stretch. Then, I place the treat in the corner of her mouth, where there are no teeth.
We also stop every so often on rides to share water (and whiskey, a human treat!), and when we do, we give our horses treats sometimes. The horses must stand side by side and not make faces or nip or kick at each other. They are lovely about it most of the time now.