Just put your panniers inside a reusable grocery bag so you don't have to leave them outside the store where the panniers might get stolen. Stick the reusable grocery bag in the cart on the folding kiddie seat, and shop as usual.
When you get to the checkout, either give the panniers to the bagger, or bag them into the panniers yourself. Places like Lidl, Trader Joes, and Aldi all make you pack your own bags anyway.
My son lives in Baltimore and does his warm weather grocery shopping this way with his Cannondale R900 with a rear rack, and 1994 vintage red Cannondale panniers. He will also use a plastic milk crate bungeed to the rack for larger items like gallons of milk or laundry detergent.
I do like the kitty litter bucket idea, sometimes you want to be able to seal your cargo in a water and airtight container.
Last edited by Keefusb; 03-08-23 at 08:43 AM.