If there are other things I need in that aisle, or the aisles on either side, I am more likely to get those things and then come back to that product. If not, I am more likely to politely say "Excuse me." If an aisle is very crowded I am also likely to pick up stuff in another aisle, and then return. I do my big orders at Walmart, because I have to use the electric scooter carts they have, and I usually tug one of their big regular carts along behind. That way I don't have to load the car and then come back in for another load. Going through the store riding one cart and hauling another takes up a lot of floor space, so it is best to put off the crowded aisles, until the crowd thins out.
Although I prefer to avoid social occasions like parties, I can almost always handle store contacts. If something is too high up or too far back or too low and far back (bad knees and back make it hard to bend), I will ask for help. I can manage the local mini marts, because my favorite one has small shopping carts, as well as hand baskets. Since I am not in there as long as I would be in the Walmart, I can walk that smaller store while holding onto the cart.
I realize that a lot of us on the spectrum have trouble with simply saying "Excuse me, please," but the people you need to say that to are not likely to bite your head off. I used to have a bigger problem with this when I was younger, but after many years of temping, I got more used to dealing with strangers. I still don't care for it, but I can handle it much better. And, I am willing to be polite and civil when dealing with strangers. This sometimes works when dealing with difficult relatives and acquantances. I can't stand my older brother's wife, for good reasons, but am always polite and civil when I occasionally see her at my father's house, so things have gone well. Hey, as long as I don't have to spend a lot of time with her, or horrors, live with her, I'm cool with polite and civil.
Just keep your own cool when you need to speak to people, and remember, we on the spectrum are all:
A Different Drummer
If a man does not keep pace with his companions,
Perhaps it is because he hears a different drummer.
Let him step to the music which he hears,
However measured or far away.
--Henry David Thoreau