What you need:
Our supermarket had small shopping trollies for the littlies for a while (they had been removed however I believe they are due to return). Cakes took a delight in going shopping and kept all her own items in her trolley. We would tell her what was on our shopping list that she was needing as we came near an item. She chose the flavour, type or amount of each item she was to buy. Though her trolley was much smaller it was often as full as ours. At the checkout she helps with paying by pushing the green button on the EFTPOS machine and always gives the checkout person her shopping card (the flybys card). The most improtant part of any shopping mission for Ckaes is getting the receipt (if it comes with money that is quickly returned to us as the piece of paper is much more important. She has understood that you must pay for an item before you can open it or leave the shop for a long time now which is very helpful in preventing tantrums for the much wanted Scooby lolly.