How to not over-snack when you hang out with friends?

I'm not overweight, but I'm around the 80th percentile and I'd just like to lose around 15-20 pounds. Anyways, I've done a lot of research about weight loss, and I think that I exercise and eat pretty well while I'm at home. However whenever I hang out with friends (which is usually 2-5 times a week), I find myself munching on whatever is at hand, regardless of its nutritious value. Anyways, I was just wondering how to avoid eating bad foods when they are right in front of you. Thanks!