I sometimes find that I buy things immediately off the web because I'm worried I'll forget about them in a day or so. Unfortunately that's not the best way for me to manage my finances.
So how about a bookmarklet, or even an app, that lets you grab an item (with all the relevant ordering data) and store it for later revisiting. It could build up a shopping list, keeping a tally of the costs that you could then revisit at your leisure to buy the items.
Perhaps even set a budget so that it will only let you order a certain amount of stuff in any given month.