Mine have thrown some shocking tantrums in stores, I feel your pain. Can you take someone with you the next few times, so that if he cracks it you can just leave (but still have someone to mind your trolley or finish the shopping).

Or you could promise a treat at the end, but you have to buy all the other things first? Online shopping is pretty good though. Even if you get groceries online and go out for your fruit and veg, then there's less at stake if you need to leave.

Distraction might work too...snacks? A toy from home? And don't shop when he's tired at all? All the best. xo