I also think it’s beneficial to give smaller rewards for hard days. If I am struggling a lot with my anxiety, depression, PTSD, or just a rough day, I try to reward getting what I can buy getting takeout food or ice cream that day. I may also reward myself during the activity (such as a Starbucks drink while doing work).
When I’m not in the mood I put music I want to hear and love.
I found that exercising and reading about very different topics makes me a lot happier.
Perhaps it could also work for you