Not sure if this is what you are asking but paper wallets aka bitcoin cheques work great.
Make a few dozen and put 0.1 or 0.02 in them or whatever you need. When it comes to paying, just hand it over.
The shops are small shops most of them sell eating products which can be an arbitrary small cost, problems come when such small amounts are involved with paper wallets, if people want to eat from multiple stalls they'll have to carry dozens of paper wallets of fixed amounts.