Members of your club can put charges from the Snack Bar on their accounts. The club then bills the members according to their own timing (typically monthly). Invoices then appear on the Members Payment Screen.
Once you have logged in you should go to your manage account screen:
This screen should be familiar to everyone since you use it to pay your dues, buy guest credits, pay for parties, etc. What may be unfamiliar to you is the Open Invoice area at the top. There are now check boxes next to each invoice. Select the invoices you are going to pay. (if you are purchasing anything else it will be tallied up and can paid for at one time.)
Simply choose credit card to check out and at the next screen enter in your details.