So sorry to say this.......staying at home!
It's meltdown at the roundabout before the mall for us so we cannot get near the shops with DS, he is 3.5yrs old.
Have you tried the toddler reigns?

leesh or in the cart or carry her

There is a special harness made for special needs kids. Child Harnesses by elaine if i remember correctly. They are pricey but they are sturdier than baby harnesses. I use that when he is walking. Other than that, i kept him in a stroller until he got his adaptive wheelchair. He now rides in a convaid easyrider nontilt. He was in a regular stroller until about 4 years old. I got a lot of looks but i either ignored them or glared at them until they looked away. Oh and the comments came in rushes but i just explained that he was special needs to those that were simply inquiring out of curiosity and ignored or told off those who were being mean. At the end of the day, all that matter was his safety. That is also how i got his wheelchair through insurance. Him being a flight risk and a danger to himself (e.g. may decide to throw himself down in the middle of the street) was the justification for the chair through insurance. In turn, i make sure he gets plenty of exercise at home so that the time in his chair is less than the time out. We will also go for daily walks to the corner and back a couple of times.

I just don't even try to go anymore. I grocery shop online and if I do have to go to the shops I make sure its a daycare day. I have tried the reigns but it seems to make no difference as its just meltdown after meltdown and it takes a couple of days to come back down. I recently hired a stroller for larger kids which seems to help but get odd looks and dirty comments from people about having a child that big in a stroller. Mind you he is only just 3yrs but is the size of a 6yr old