When purchasing a round of drinks, establishments generally aren't fond of digital payments and are usually short on change as most prices end in a 9.

What's really appreciated is if you bring a coin purse, and count out each total in change (denominations up to and including 50p - pound coins in extremis) on the bar so the staff don't have to provide you with change.

For additional kudos, do this on a Friday or Saturday night when the bar is four deep. The patrons will appreciate your effort and respect for the public house financial system, and often chant words of wisdom at you, rendering you a local hero.