We often plan to cook a meal together, usually on Fridays when we have a bit more time/energy. Something with flavors/textures that are different from our regular meals, or that requires more elaborate preparation...or go the opposite route, and make it an "easy-prep" meal so you can reward yourself with a night off from cooking. Still food-related, but more about variation than about junk food, plus the experience of enjoying a meal together.
Novelty is highly rewarding for me -- new places, new activities, and just shaking myself out of my usual habits. So I try to 'treat' myself to new experiences in easy ways, like finding a new park to take a walk in, new route to ride my bike, new-to-me activities, etc.. Finding local opportunities for free/cheap entertainment and engagement has been a fun challenge, and led to lots more options for treat-like things.
Find things to do that engage new parts of your brain. For me, it's often making things with my hands -- I get engaged in it in ways that are very different than my usual tasks require. I guess this isn't a treat so much as a way of spending my time that doesn't leave me feeling like I need to be treated.
Call a friend just to talk.
Throw the ball for the dog.
Make myself a mug of tea.
Light a fire in the fireplace.
Eat breakfast for dinner (or dinner for breakfast).
Read a good book.
Plan a future adventure.
Make art.
Sit in the sun.
Go for a walk.
Wait fifteen minutes and see if I still feel the need for a treat.
