I think everyone who diets has that loss of resolve as the day goes on. One thing you can do is eat most of your protein and fiber in the morning, in portions that satisfy you and stay within your calorie limit. For example, tuna canned in water, drained, and mixed with just very little mayonnaise and then heaped on some high fiber crackers - with some chopped olives and capers - will be high in protein and savory. The fiber is really helpful because it makes you feel full, and the protein helps, too. Make the protein as low in fat as you can but as high in protein grams as you can. Then you end up with something that is not too caloric, giving you more 'bang for your buck.' Also, make yourself a cup of aromatic hot tea. One thing you want is lots of pleasant aroma to combat that cafeteria-cooking-smell-atmosphere.
It may take a while to build up a menu of food choices that will satisfy your sensory needs. However, they ARE important. I never can get the same satisfaction from something that is cold and pale and bland. That reminds me: hot, steaming soup (make your own and bring it for the microwave) is very low in calories, or can be, and it's easy to control the sodium when it's your homemade soup.