My son is much younger but we are working with astory book about shopping so he knows he won't get anything on this trip, it lets him use a check list to show what we are getting. It also tells him what he can have when he gets home if he's good. I also have an outing only bag of toys that he plays with while we shop!

CBP is correct. Be consistent and mean what you say. If there is one thing Spectrum kids get it's consistency.
Another possible trick, since he's 13, give him a budget. Let him carry the cash and decide what he wants. Then the cash will limit it, not you. Oh, and that has to be consistent too.

Perhaps if you gave him a task to do while he was at the store -- like be on the lookout for the pasta sauce or if you know how much a product you need for a recipe, explain that to him and when he finds the product, ask if he's gotten enough for the recipe or if you need more. If he thought there was more to the event than just getting a trinket, it might help occupy his time and energy. I do this with my toddler and she seems to be distracted by the game and loses focus on getting something.

@A MyAutismTeam Member...ive had him take his trinkets with him, but they loose appeal once were in the store...I have to remind him before we go in why we're shopping and he is not allowed to ask anything...because the answer will be no...he still will ask numerous times and the result is the same, crying and moping around...not a pleasant trip for sure...he can be relentless:(

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A MyAutis...

LEGOS. "Can we look at Legos?" "Can I have Legos" "Do we have money for Legos?' This is how we finally had to handle it. You have X amount to spend each month when you spend this, that is it. No more. You can spend it all at once or a little at a time but once it is gone it is gone. Then before entering the store (when we aren't getting anything) this is the conversation, "You spent you money and for this trip you get nothing. If you ask the first time you get a reminder the second time when we go home you LOSE something you bought." The hardest thing is sticking to your guns(so to speak) None of us like meltdowns and tantrum, especially in public.(the stares, the glares, the feeling that we want to strangle people...lol) But No has to mean NO. He can't mope forever, as much as we hate to see them unhappy they have to learn that you can't ALWAYS have everything. I am blessed to be able to leave him at home with someone (which we did for 2 weeks)When he realized it was better to be included then left behind he didn't ask...as much. He still asks...I tell him NO and he knows" That is my final answer." (everyone's situation is different and what works for me may not work for you but I hope it helps.)