It sounds too me like it's a matter of having habits with certain activities, which trust me, there is nothing wrong with that! Pizza parties make studying SOO much better, and movie night, or girls night with chocolate and wine is always fun! When you think about it though, we associate those activities with food.
You need to find a new activity, and don't bring food into it! Something that has worked for me, is video games. I'm not sure if you are into video games, but if you AREN'T, that may be a good thing because it's an opportunity to try something that is new and fun. However, like I said though, DON'T bring snacks into playing video games or else you will start associating snacking with that too.
Even a change of environment might help you. I'm not sure what you live in, but let's take watching TV or a movie for example. Maybe watching TV in the living room is where you have always sat down with your favorite snack and soda and just eat for minutes on end. This is a habit that has been developed over time. Now, let's compare this to watching TV in your bedroom. I know typically when I watch TV in my bedroom it's because I am either just waking up, or about to go to bed. I normally don't eat when i'm just laying in bed. Maybe now is simply the time to start watching more TV in bed, or wherever you have a TV that you don't normally use. Make it a habit to not bring food into the equation.
Again, I don't know how many TVs you have, and I don't know your setup, but these are just two things that have helped me with my late night snacking problems.
Personally, when I get home from an exhausting day of work, I LOVE sprawling out on my couch and going to town on breyers oreo ice cream. When I started my diet, I knew that had to stop. I came home, sprawled out on my couch, and realized that I wanted my ice cream. Basically, since this wasn't an option, I just went straight to bed.
When it comes to breaking habits, and creating new ones, there's always good days and bad days. This is just one strategy that has really taking the edge off for me.
Guitar hero is my favorite because it's so involved, there really is no time for snacking! (and yes, I still play guitar hero... lol)
Sorry if this was long/redundantish, but I hope it helps you!

Best of luck!