It may be physically difficult to go back directly from eating mostly junk to eating clean using willpower only.
I was looking for a surrounding factors to help myself with this return. Tomorrow there is a football game which is very often very good stimuli to behave well.
So tonight after dinner and after goodbying my friends I am planning to go to bed and rest. Tomorrow if I feel good enough in the morning I will attempt to do a workout. If not, I will just focus on getting ready to play football. From wednesday onwards I should be able to be back in my ascetic routine.
The idea is not just to get back to work but to do it mindfully and effortlessly, saving willpower for harder times.