Your husband has a point, only in that I just give people a wide eyed "dirty look" type stare when they do that to me. I mean, when I see someone's kiddo acting up, I know they are probably already embarrassed enough so I don't stare at them unless I think I can help out or unless they are hitting their child or something. The polite thing to do is pretend you don't notice, then wipe the blood out of your eardrums after you round the corner. (ha ha, only kidding)
There are so many different methods of discipline; Don't do time outs, Do time outs, etc. Anyway, it really doesn't matter what consequence you choose, just do something quickly, and know what you will do BEFORE you enter the store.
By quickly, I mean that you look him right in the eye and say please stop doing x or I will do y. You may want to allow a "by the time I count to 3" statement to give him a few seconds to change gears. Then at the time you hit 3, DO whatever you said you would do, CONSISTENLY, without fail, every time.
This will actually help the child learn to control their own temper or actions. He is obviously testing you and asking for a limit, so this is a great opportunity to teach him just exactly what will happen.
Another thing this helps with is your own temper. If you are nipping things in the bud, they don't escalate to the point where your child is being trained not to listen to you because you keep repeating yourself and doing nothing when they don't listen, and the top of your head is not blowing off because again, you are not repeating yourself over and over and being ignored.
You have to gauge each situation, but it is also helpful to find a distraction that always works. I use Mr. Hand from a discipline book I was reading. They said it always works, and I KID YOU NOT, every time I pull Mr. Hand out and have him start talking to my child, it pulls her right out of the tantrum. I usually opt to use him instead of a consequence based upon the emotional"ness" of her tantrum. If she is really totally in emotional freak out mode, I feel the distraction is more appropriate than the consequence. Or other situations where the consequence is not practical or appropriate. You have to judge each sitation separately, and quickly! LOL
Here is what I do for a consequence in stores. I tell her she is going outside to time out. She knows she is in trouble because my face and demeanor are serious, and I take her strongly out of the cart and hold her kind of stiffly (not hard or anything!) and walk briskly while telling her that's it, we are going outside because you are not listening to mommy. Then we stand together outside of Publix and I make her face the wall while I am crouching down beside her. We're facing the wall because if she is having fun waving to people going by it's not very effective. It truly doesn't matter how long, you can start with two seconds! That always snaps her out of it and then we can finish shopping, and she knows there will always be some consequence, taking something away, putting her in the cart if she's out, going out of the store, etc. Start now, and he'll know what is expected of him before he turns the dreaded 2!!
I always bring 3 or 4 snacks, toys, juice into the store, and give things to her spaced out so we always have something new. I let her put cans into the basket, hold the list or a green pepper, stop and play with a ball or stuffed dog that they sell, get a balloon when we arrive instead of when we leave...etc. And my list is always very organized so I can get in and out. Just to keep her from getting bored. Then I talk to her about what I'm doing the whole time we are there to keep her involved. "Oh now this is dairy, that comes from cows, can you say moo?" lol
Hope that helps, and hey, I have a friend with 2 close in age who always act up at the store. At least you only have 1! :-)