Where does your baby sit while you grocery shop?

I recently switched out my sons (who is 8 months old) infant seat to a convertible car seat so i no longer have the option of bringing him in the store in his car seat.

He’s also over 20 pounds and extremely hard for me to carry through the store on my hip. He can sit up well on his own but I’m afraid of putting him in the carts. I don’t want to bring a stroller because that seems pointless.

Any suggestions?