One way of thinking that really helps me is focusing on the amount of food you get for your calories (kinda like a volume/calorie metric). For example, a container of sugar-free jello is only 10 calories. Add a tiny bit of light/no-fat whipped cream to that for 15 calories, and you have a pretty decently sized dessert for 25 calories. A lean meat turkey hot dog? 45 calories. An original boca burger? 90 calories. A serving of unsweetened apple sauce? 50 calories.
Finding these sorts of food that provide voluminous bulk without massive calories will really help to fill you up. If you eat 2k calories a day, imagine how many smaller items you can eat throughout the day! Studies show that most people tend to eat constant amounts of volume to feel full, regardless of how caloric that volume is. So, when I start watching my calories, I focus on maximizing the amount of food for the number of calories I have for that meal.
For example, if breakfast is 300 cal: you could do a piece of sprouted grain bread (90 cal) with an egg on top (65-75 cal), 17 mini saltines (70 cal), 2 cups of water with lemon in it (<5 cal) and 2 slices turkey bacon (70 cal). That's a lot of food for about 305 calories, and there's no reason that won't fill you up until your late morning snack. :-)
Also, water doesn't really fill me up unless I add some flavor- I like to make some lemon or cucumber water (just cut some up and throw it in a pitcher with water, let it sit overnight), and that really helps me fill up.