Nope, I never cheat.
See, if I say I am not allowed something, I will want it 7032470937409 times more. I believe this rebellious tendency goes back to my childhood. I've always hated following rules, so why would I place any on myself? I am allowed anything I want, as long as it is part of my calorie count for the day. Ice cream? Cookies? Crackers? Sure, if I really want it...
Here's what keeps me eating clean most of the time:
Clean, nutrient-rich food makes me feel SO much better than processed junk. I hate feeling sluggish. A balanced, healthy lifestyle keeps me from frequently getting sick. Besides the health benefits, I can eat more FOOD if I am not indulging in so-called treats... and I LOVE to EAT. A Blizzard from Dairy Queen has around 600 calories in a small -- that's two small meals for me. I'd rather eat those meals, dangit!
Now, if I DO eat more calories than I burned on a given day, I don't beat myself up over it, I don't decide to furiously work out for hours to burn off the excess, nor do I try to make up for it the next day. I have done all that in the past, but it only leads to feelings of despair and failure. We all are cursed with a common condition called being human. We're beings, not machines, and no one is perfect.
There ARE a few foods I just can't have in my house because I KNOW I will eat them until they are gone, so I just don't buy them. If I want them, I will get a single-sized portion (small box/bag/whatever) and be done.