This summer, I started to keep a pair of tennis shoes in my car. That way, if I ever want to go for a walk and don't have the right shoes with me, there's a pair available in my car.
When I get a sweet craving in the evenings, I eat a package of 3 dried prunes and drink a cup of water--that way, I've satisfied my sweet tooth, and I've added fiber and water to my diet. Try it, you'd be surprised how well it works--I know I was.
When I want to snack, especially at night, I find that eating fruit takes away my sweet cravings. I especially like eating oranges because they are not only tasty, but they take some time to peel and divide, so it actually takes a while for me to eat my snack.
I tell myself to go to the gym and just do at least 30 minutes of cardio--once I've done that, I often find myself doing some strength training or doing another 15 min. of cardio. Sometimes the hardest part of exercising is getting started!