For me, it's all about thinking about how the food will affect me, and if it's an appropriate time to eat that food.
My example- I love poptarts. I know they're junk, and I know I could be eating something homemade, etc etc. But I looove them. And so does my husband, which means we have to have them around the house.
I found that if I get up and go to work at 7, and eat a poptart, I will be so hungry that I'm shaking by the time 10AM rolls around. Then I'm more likely to eat a ton of stuff I should.
So I usually have a poptart, or a half of one, at the end of the day for dessert. That way I still get my treat, but I don't need to keep myself full, since I know a poptart won't do that.
So...if you have a snickers because you need a snack, keep in mind that it may not keep you full the way you need it to (that may have been your problem the day you ate the burrito and pizza? I know if would have happened to me), but if you have some extra calories and want a treat, it's up to you