Great idea for a group! I have been a dedicated mugger for over two years, and as I begin my morning T ride out to Medford I invariably stop and fill up with French Roast at City Feed.
Often the morning line in City Feed can be quite long. Wouldn't it be a great idea if they had a money box near the coffee where people just looking to fill their coffee mugs could drop in their $1.50 and avoid the line of "non-muggers." This would reward those of us who bring our mugs and it might even help City Feed sell more coffee, as I have often skipped my coffee when the morning line was too long and I was in a hurry.
I have seen people do this whether there's an express line or not. If you haven't OK'ed it with staff, I suppose it's a bit presumptuous, but if you know what the exact cost of your fill-up will be and you leave exact change on the counter where the person at the the register can see it, I don't think many would have an issue with that. I almost always pay with plastic (easy to keep track of) so I can't put it to the test, but if you're a cash-carrier, it seems like an easy shortcut.