Yes, you have to plan for snacks, and if you make sure they're healthy and fit into your plan (whatever it is, then snack away). I know I am very vulnerable to night time snacking, since that's when I get back to working on the computer after the dinner-kids-straightening up drill. I usually leave myself 300 calories for after dinner...yes, I know eating at night is considered a no-no, but if I don't plan and have small snacks, I will just get cranky and eat everything, and I'm often up till 1 AM. That is a lot of time to eat bad food, so I just plan for good food instead and...it's important...it works with my lifestyle.
I usually try to look and see if I need carbs, protein, or fat and try to choose snacks based on what category I need to increase (yep, one night it was just sliced turkey).
Just be "mindful." That's my new word for diet and other areas of life. Mindfulness is underrated.