I believe truly in the "80/20" rule. I eat very healthfully 80% of each day. I include whole grains at every opportunity (I limit white/processed sugar, flour, etc as much as possible), eat lots of fruits and veggies (especially dark, leafy greens), eat lean sources of protein (legumes/beans, fish, tofu), and use non-fat to low-fat calcium products. However, each night I have a snack. My snack ranges from a small bowl of hand-mixed trail mix (raw walnuts, raisins, plain cheerios, chocolate chips, etc) to two chocolate chip cookies (I make them "healthier" with whole wheat flour, no eggs, half butter/half plain yogurt).
I noticed during college that if I did not have a snack, I could not sleep well. Eating "too" healthfully was actually causing me to have "unhealthy" sleeping patterns. By incorporating a 200-300 (max) calorie snack, I can sleep better at night.
This is not something that I would recommend (I am NOT a Registered Dietician), it is just what I do.
Anyone have comments or tricks that they would like to add? Post them here :)