Don’t go into well known coffee chains. Use your mobile phone as a mobile Wifi device.
Both of those are sometimes not an option.
I always use a small, independent coffee shop in town, which doesn’t have wifi. The O2 shop the other side of the passageway into the precinct has free wifi, but it’s a) very low powered, and drops out with annoying regularity, and b), is annoyingly nanny-ish, censoring websites for seemingly random reasons.
I was therefore delighted to discover that Natwest Bank, the other side of the high street, has a much more powerful wifi, that doesn’t come over all nanny-state, and didn’t require any more personal info than most other free wifi sources.
Worth checking to see if there’s a handy branch nearby.