Give up the "I blew it, so I might as well trash the rest of the day" attitude. I believe this is just our way of giving ourselves permission to continue to eat badly. Did you make a bad food choice at lunch? Then so be it. Eat a healthy, responsible dinner and stay on track. It makes no sense to say, "Since I made a bad choice at lunch and went over by a couple hundred calories, that means I should just eat a couple thousand more today because now it doesn't matter." So don't give yourself permission to do that.
Also....just for me.....I don't call bad food choices "slips" unless it really is one, like accidently using the full-fat dressing when I meant to use the fat-free. Eating a bag of fries or choosing to have a candy bar isn't a "slip" to me; it is a conscious decision that I made and I am responsible for me. That doesn't mean I should beat myself up, but it also doesn't mean that I should label it an unintentional accident, either!
So that's my advice. Don't give in to the all or nothing thinking that there is nothing between being perfect and an eating free-for-all, and take responsibility for what you eat. And be aware that I consider items like skinny cow ice cream, baked lays, and the occasional slice of pizza to be perfectly on-plan FOR ME. It doesn't work for some people, but that's just how I roll.