I've been fighting the same 10-15 pounds for the last five years. (Gain it. Lose it. Gain it back. Lose it again.)
I tend to succumb to junk when I'm stressed. So ... to try and combat that, I try to keep a healthy supply of low/no-fat goodies, fruit snacks, fresh fruit and vegetables on hand. If they are there, I will get them instead of junk!
Also, WALK, WALK, WALK. If you drive, park farther away on purpose. Ride the bus? Get off a block or two sooner. Elevators? What are those? TAKE THE STAIRS.
I'm amazed at how much those two things alone can do.