A small, low protein, high carbohydrate bedtime snack, such as juice and cookies, eaten about an hour before bedtime, can help you fall asleep sooner. (Pizza does not qualify.)
On the other hand:
Studies indicate that foods with large amounts of the amino acid L-tryptophan help us sleep better. These include warm or hot milk (but not cold milk), eggs, cottage cheese, chicken, turkey and cashews.
Try both food theories, and see which works best for you.