Sorry, slightly baffled. You're allowed to accept a drink from a stranger, but your dh isn't allowed to buy one for a stranger? What's the diff?
FWIW, I wouldn't do either, although will readily accept any drink offered to me by a friend, either male or female
On the other hand, when I moved to Mexico in 93 I was told in no uncertain terms not to accept a drink off a bloke as it was tantamout to agreeing to have sex with him. To the point where, if something bad had then happened, the police would have said "so? You accepted a drink from him".
Now, I'm not suggesting that that is right, or that we should live by those standards in the UK, just pointing out cultural differences. But I would not accept a drink from a stranger in this country, as I think it sends out the wrong message regardless of what message you think you are sending, and I wouldn't buy one either. Nor would I expect dh to be buying drinks for random women, or accepting them. What is sauce (or wine) for the goose is sauce (or wine) for the gander.