Like others have said: pick up and carry on. There's no use wallowing on what happened, and 'just' one setback doesn't mean that everything's lost--it's accumulating the setbacks that creates a real problem.

If you need to (and can), plan your next few days according to "avoiding temptations". For instance, my biggest downfall is physical inactivity (watching TV and reading count in that; grading my students' papers too, alas XD), so if I'm not sure I'll be able to get back into the saddle, I do my best to plan a day of going out, walking a lot in town, visiting a museum, etc. (Of course, it works well for me because I'm never tempted to eat on the run, so I won't buy bagels etc. while outside; if this doesn't work for you, you have to find sommething else.)