I have a really tough time with this too. I will find myself mindlessly snacking at night when I've quieted down and aren't doing much. If it's my time of the month or I've had a stressful week or any other situation where I know that I'm not going to be able to fight the cravings, I scoop half my veggies or part of whatever else I'm eating for supper and stash it for later so that I'm not going over my calorie limits.
When I really don't want to end up snacking that late, I make a big mug of herbal tea and sip it slowly. That way I'm still putting something in my mouth.