Great question, Ria. In small urban apartments there's no room for a proper shopping trolley. We want something that will store away flat or hide in a closet. And of course trolleys and carts are a virtual necessity in the city. Unless you shop every day or just always take a cab from the grocery back home, it's hard to tote all those jars and milk jugs home.
Here are a few good ones we've seen lately. We're especially impressed with the Riesenthel; it folds up smaller than a travel cosmetic case. It's completely flat; you could store it between the refrigerator and the cupboards, or on the shelf like a book.
The Sur La Table model is very different; it's just a frame for you to hook your own bags on. We like the flexibility this gives, however, and it's quite small.