Planapple lets you archive items that you no longer want in your trip. And if you change your mind later, you can always bring them back from the archive.
To archive an item, click on it to go into its details page, and then click the “Remove” button near the top. Archived items won’t appear in your item lists, though they’ll still be included in the Trip Updates.
If you want to see the archived items in your trip, click “Removed Items” (on the left side of the page). From there, you can click the “Restore” button to return the item to its original section and category.