Little wins can be pretty much anything
The details of little wins aren't important. What's important is that you recognize their power and the momentum that they can potentially develop once you get on a little winning streak.
To break your habits, and build new ones, you have to become aware of the process. Piling up little wins not only allows you to become aware of the habit you're trying to break; it institutes a plan for you to break that habit. This could mean taking the stairs instead of the elevator, choosing water instead of a soft drink, or just getting a whole-grain bagel instead of a regular one.
For example: you could swap out the donut for a large coffee, and opt for skipping breakfast completely, which might be a good strategy to try. Or, instead of the donut, you could just have a fiber-rich bagel with a little bit of peanut butter.