Sorry to be the big bad voice of doom but I don't do this! (Anymore at least).
Why blow it before you've even started for the week... you only make it harder for yourself to lose?!
I used to do this and it definitely slowed down my losses, and reinforced the "naughty food as a reward" feelings I've been trying to get rid of my whole life.
Now I just have a really nice SW friendly meal and maybe syn a glass of wine, or I treat myself to some new make up or a handbag, for me personally its just not worth it.
Each to their own though! xxxxxx