Economies of Scale
On my way in to work this morning, I had a few extra minutes so I decided to get my bus change then rather than waiting and risk missing the early bus to get home. I stopped in one of the convenience stores and wandered around looking for something that wasn't too horrible for me, and my eye happened to fall upon a box of Cheez-Its. I love Cheez-Its, and the vending machine in the basement charges some ridiculous price for them, so I picked it up.
Well, the price wasn't well marked on either the box or the shelf, and it turned out there was a good reason: by the time I got done paying for it, I'd have been better off buying the extortionately-priced bags from the vending machine, by about a quarter. This isn't much, but I guess there's a reason it's called a "convenience" store rather than a "good prices" store.