I keep some single-serving snacks in my desk at work - granola bars, trail mix packets, etc - but I don't keep a lot of snacks and I keep an eye on the time. So when I start getting hungry at 11, I tell myself "Hmm, you go on lunch in half an hour, may as well wait." If I get hungry at 2:30 pm, I allow myself one snack. This only really works during the work week though.

At home, I just don't keep a lot of snacks and I try to just cook one meal's worth of food at a time. If I have food ready to microwave in the fridge or if I have snacks lying around, I will graze constantly.