I spent a lot of time when ds was little playing train sets, farms and taking it in turns to build towers to be knocked down. He had a couple of sets of colourful blocks that I'd use to build fields, houses, stations etc. He was quite a bit younger when we did this though as I was a SAHM at the time. I also had no idea he had ASD at that time.
I would say that your ds's idea of fun play might be different from NT play and you can't really make him enjoy something that he doesn't. You also can't assume that what he does at home with you, with your particular toys, will then be taken and used in a different setting with different people and different toys. That's not to say it's not worth doing of course! Just that it's not always as simple as if I play shops with ds at home he'll know how to go to school and play shops at school.
I'd also say that kids grow up alarmingly fast now and seem to get into super heroes and that sort of thing by 6. They definitely won't be playing ice cream shops in the playground, more like haring about being characters off the tv or playing football.
I definitely think having play dates and having fun things set up for them to do together is a good idea, I found this worked best for ds too. Treasure hunts, colouring in of favourite characters, lego building, obstacle courses and making dens are all things I remember doing. Also chatting to the kids and their parents and finding out the sorts of things they are into and that you can introduce to ds can be really helpful. At not much older than 6 they started getting into computer games, the lego games were very popular back then.
I would recommend a kids football club if there's one around, ds went to one for a while and the guys running it were brilliant. He was never that interested in football but it helped with coordination, it was very structured and once the kids got to Yr 5/6 and ALL the boys were playing football every single break time it gave him the opportunity to join in and have some idea of what to do. Having some football ability can be extremely useful (although ds didn't so would happily go in goal as no one else ever wanted to!)
The most useful thing I did for ds was to get to know the other parents well, I joined the PTA and had lots of playdates. It is often much easier for a child with ASD to build a friendship away from school on a one to one basis than in school where there are lots of other kids to compete with IMO.
DS is now doing a degree apprenticeship in software engineering and loving it. Computers make more sense to him then people!