Let's assume you operate a vending machine with various items, doesn't really matter what items.

Traditionally, a vending machine asks for a selection, than asks for payment (or the other way around) and then it hands you the selection.

Though, if you were to make vending machines that accept bitcoin as their only payment method, you could have each item have their own bitcoin address (each item in each vending machine will need its own address, which is not a problem because there are plenty of addresses, even if we need quadrillions of vending machines).

If a customer wants a product, all he needs to do is scan the QR code, and accept the payment of that code (price is already included in the code). Since the code is unique to the vending machine and that product, the vending machine will know when money arrives at that address, that it needs to distribute the product, and at the same time, it can keep track of how much is in stock.

The advantages:

• Keeping stock inventory is easy, you will know at any time exactly what each vending machine has in stock (excluding any malfunctions, such as erroneously distributing too many or too few items). Not only can this make restocking more efficient, as you can plan more efficient routes at more efficient times. But you will have all the data about when and where something is sold, so you can supply much better to the demand in real-time. If you plan carefully you will NEVER have any vending machines out of stock on any item.
  
• you don't need to manually pick up the cash. (you need to restock of course, but to pick up cash, unless you do it yourself, you need expensive professionals to pick it up).
  
• It uses only very simple materials, and could potentially be made DIY with simple materials (raspberry pi/arduino or something similar, a few QR codes, some small electric engines to drive the distribution machinism, and that's basically it. The hardest thing is constant wifi/3G to look for transactions on the addresses it needs to look for. (this is necessary because otherwise it doesn't know when to distribute an item).
  

Disadvantages:

• Internet connection is not optional. (I suppose you could technically also turn it into a WiFi spot, turning a disadvantage into an advantage, as a WiFi spot might draw more customers, the costs to doing this need to be weighted against the benefits though)
  
• This system prefers stable bitcoin prices, as you have your prices fixed in bitcoin unless you use small programmable displays instead of fixed QR codes and remotely update the price of the item whenever the price of bitcoin changes too much or rig the system in a way to easily do currency exchanges on the spot and calculate the right price on a per-transaction basis (which slightly complicates the software-side of things)
  
• Mixed payment options would make all the advantages obsolete, so you would only really be able to allow bitcoin. (or any other crypto, but allowing more than 1 crypto would complicate things for the user because there would be too many QR codes, although using custom QR codes (with a logo in the center) might allow up to 3 crypto options, if you assume the vending machine is in a location where the expected customers are tech-savvy enough to understand the concept.
  
• would only work in areas where the public is tech-savvy enough to use bitcoin in the first place.
  

An experiment could be done in japan.
Large vending machine operators would probably benefit most, because they would benefit the most from the smart restocking and the amount of money they safe on not havng to manually transfer huge amounts of cash.