1) Vending machines are of the devil.
2) Parking farther away from the building and taking stairs instead of the elevator may sound hokey, but it really does burn more calories and can also serve as a bit of cardio to keep you in shape. Just be consistent with it!
3) If you're in an office, keep healthy snacks at your desk so you aren't as tempted when others bring in goodies. Remind yourself that you may "deserve" a treat, but you deserve a healthy body MORE.
4) If someone needs an errand run and you have a spare five minutes, offer to do it for them--deliver a hard copy of something to someone in another area of the building, etc. This will not only give you a bit more exercise, it will keep you from getting burned-out by looking at the screen all day. (And it may earn you some brownie points too!) Obviously don't spend all your time running around, but getting up every hour or so is a good idea anyway.