I often thought about treats and rewards as interchangeable terms, but lately I’ve realized that they are quite different. Rewards imply expectation of a certain performance, and this makes me a bit uneasy, particularly in the parenting context. I think that developing a dependance on external approval, especially of performance rather than effort, can be counter-productive. It removes the sense of control and agency. For adults too (I am thinking about myself here), the expectation of a reward can substitute the original motivation for doing something.
On the other hand, a treat, in my mind, is something entirely positive. It is doing a pleasant thing for someone (or for oneself) simply because we want the person to feel good. There is no expectation that a treat has to be earned or that it is due regularly. Actually, I think that regular treats are good, but they have to different in nature from one another to avoid Hedonic adaptation to their positive effect.
With my daughter, I like celebrating seemingly insignificant milestones like the first day of a school term or the first day of vacation by doing something outside of our daily routine.
For myself, a change in activity is often a nice treat in itself. I think I somehow developed a pool of go-to treats that I can rotate and that I know would be good for me in general, like reading a non-technical book while eating lunch (my current one is the biography of Leonardo da Vinci by Walter Isaacson) or working on a personal photo project for a couple of hours a week.