I'm not a fan of the hand-clenching method of shopping, but I can see how it'd be useful when you are shopping with multiple children. With our only child, we just involve her in the shopping process. At certain ages where she was riding in the child seat, we'd just keep up a constant chatter with her about what we were doing, and handed her the groceries to place in the cart (anything that was less than 5 pounds and unbreakable, anyway). At later ages she wanted to push the cart, or ride in the specialty carts (Home Depot's race car carts remain a favorite) while I wheeled them around dangerously close to product displays. At other times she's helping find objects, checking items off the list (a current fave), etc.
DW doesn't do the barely-controlled cart maneuvers, but she has her own methods for having DD involved in shopping processes. An engaged child is not a bored child.
