I don't usually carry much with me whenever we need to make a quick trip to the store, especially if we're just picking up baby's vitamin D prescription. If we're driving, I usually have supplies in the trunk such as, diapers, wipes, trash bags, and extra clothes. For going into the store, I find that a small purse does the trick, especially when baby-wearing.
1 bag: alexander wang rafael
1 diaper: cloth diapers
4 items for mama: lip balm / iphone / cards / coins / keys