Almost everything that is dispensed via vending machines has a huge markup (and is rarely healthy).
However, if you suffer from snack attacks at work, consider creating a secret stash of snacks.
If you like drinking soda and have a fridge at the workplace, save a refrigerator pack in the fridge with a post-it with your name on it.
If you have a long commute, consider a stash for the car as well and avoid a quick drive-thru visit.