Man it seems like such a long time ago that in my college town in New England there was a general store and fruit market that had a cigar box parked outside every morning along with the racks of fresh produce on sale... with about four or five bucks worth of change, a couple of singles and a five dollar bill.
EDIT: well actually it was quite awhile ago... 1960s..."Please make your own change if you can manage it, and spare us both the hassle of having to maintain a separate line for produce sales, thank you."
There are some farm-stores in my area where you can by eggs, milk, butter, cheese and other items on a similar principle. You go in, get what you need and throw the money in a box (can not take it out again though). They are unmanned, open 24x7 and seem to work pretty well. Prices are good because you mostly buy what they produce (or very local stuff), the farmers get a bigger share of the end-user price and the goods dont travel far.