Unless you want to carry your items you should only stop if you are headed back to your hotel. Along with any munchies, consider stocking up on bottled water which is usually much cheaper in the store than a tourist shop.  Also, this is a good opportunity if you need change to carry for pay toilets. If your plans include doing a quick load of wash then look for laundry soap. If you are making coffee in your hotel room and want something similar to half and half you might be in luck. Also, if you need sunscreen you should pick some up because it can be difficult to find in the tourist areas and it should also be cheaper.

TIP:  Bottled water in Europe comes in many different styles. Specifically, mineral water, sparkling water and still water. Read the labels to make sure you are getting the right one. Mineral water is pretty much the same in all European languages. Sparkling water vs. still water is a different matter. Use a translation app that will translate through your camera to be able to read the labels. Ask the attendant if the bottle you have chosen is still water.