I did suggest a laptop on the stall. It rains an awful lot in Manchester and the stall isn't particularly well covered. Maybe not the best idea. I reckon password-protected phone apps that connect to secure online wallets would be best. The relatively high value of single BTCs would mean you would have to buy a LOT of fruit & veg at once, or somehow give change in decimals? Those bitbills seemed to be in 1BTC-20BTC denominations.

As someone mentioned, might not be best suited to this sort of exchange (maybe a 'subscription service' where you paid for a month's veg in advance or something.). Still, the novelty is amusing.