i usually ask a sighted-hearing person to tell me what kind of items are in a vending machine, the number that is associated with each item and its' cost. since i have certain items i like, i can easily memorize their item numbers.
soda machines are simple for me to use. on almost all of them, the first button is always coke or pepsi, depending on who manufactured the vending machine. to find out what other kinds of soda are in the machine, i'll ask a sighted-hearing person for this information and memorize only those buttons that are for the sodas i like to drink. since most soda machines are universal meaning that the arrangement and layout of buttons is pretty standard, all i really need to know is if it's a coke or pepsi machine. once i have that information, i can pretty much tell what button is for what.
when i go to the grocery store, i go shopping with a clerk who finds the items i need. i give them a shopping list in print while i use one in braille. i can usually tell if i'm not given the correct item by the weight, feel and size of the packaging -- especially since i stick to purchasing the same brands for ease of cooking (i.e. not having to always have someone read me the label directions) and the fact that i don't like risking my money on certain brands of food i may not like.