OneTrip is a basic web application for your iPhone that lets you create and keep a shopping list on your iPhone. This app was created a very long time ago, even before the App Store was created, so you will probably be able to find much better note taking apps in the App Store these days. Yet being one of the very first webapps to support creating shopping lists on the iPhone via Safari, OneTrip is still a usable app and listed here for reference.
If you want to try it out, just visit onetrip.org from your iPhone. This webapp was created by Neven Mrgan. Try with TestiPhone