Shouldn't be too hard, no. Here's how I'd do it:

Give mobs a list called, say, "shoppingcart". Have a datum type that represents the products you can buy, and has variables that describe the product; name, description, price, manufacturer, etc. Load this list from a savefile when someone accesses a page. If they've just chosen to add something to their cart, create an object of that datum type (or a subtype of that datum type) with the appropriate variables, add it to the list, and save the list back out again.

You'd need to know how to use DMCGI, lists, savefiles, and datums, of course.