On the bike: a gym bag full of wet clothes, and a box containing $49.99 in groceries.
So when you are on a bike and grocery shopping you have to get creative...even if it is a cargo bike. I find the best way (for me) is to strap a box or boxes on the bike, unless it is a big trip and I pull the trailer as well. But the thing I like about bringing a single box is that when I am low on cash--such as today--I can only carry so much,meaning I can only purchase so much. Today, for example, I brought the empty box in the store and placed it in a shopping cart. As I gathered things to buy I placed them in the box. When the box was full that was the end of shopping.