We take ours everywhere we go well before they’ve finished vaccinations (always carrying and no contact with other dogs.)
We start out with short walks to the local park, where we sit on a bench and watchlots of children, dogs, football players, bicycles etc and pup gets lots of positive attention from passers by. We do the same in the the town centre (relatively small town, not massive city). School runs, but with two of us, so one can wait outside, while the other goes into the playground to collect the dcs. We wait across the road with the pup, so they don’t get mobbed as the children come out, as that can be as detrimental as undersocialisation imho. Park at end of school day to see children running about yelling, playing etc. Different types of walks, woods, roads, public footpaths.
We go to lots of country fairs and VW shows as well, but I guess that sort of thing isn’t really doable at the moment. The advantage of them is that there are lots of different dogs and they are all on leads and friendly, as no-one takes an anti-social hound along and there are people of all ages, wheelchairs, mobility scooters, hats, umbrellas, etc. Lots of variety.
We go to several local cafes which allow dogs, one pub that allows them inside anda couple that allow them in the garden.
We also do the retail park with boot open thing that someone mentioned up thread. We have a tailgate guard and sit on the bumper so we’re close to the pup and can reward calm, interested responses.
Local pet shop - lots of fuss and treats to be had there.
National Trust property are another good option. You can sit outside the cafe with them in most places as well.
Years ago I used to go for a short bus ride with pups, but I never need to use buses anymore, so don’t bother with that one these days. It’s good to get them used to loud buses and trucks though, so sitting at a bus stop with lots of treats on hand is a good one.