A colleague went to Subway and offered to bring back lunch or dessert.  I got some cookies and he said that I could just buy him a soda at some point instead of giving him cash.

The sodas out of the vending machine were $1.25 for a 20-ounce bottle.  This was about the same price as the cookies I got, so it was a fair trade.

I instead got a six-pack of 24-ounce bottles for $3.50 at the grocery store.  The cost of two larger bottles from the store was the same price as one smaller bottle from the vending machine.

“There’s a personal finance lesson somewhere in there,” I told him.