2 more suggestions: build a page with e.g. 10 lines of input fields, one for each item to add. Empty lines will simply be ignored, this way a user can add 1 to 10 items with one submit.
Or simply put up a textarea, where every line contains an item. If you need structured information per item then let them enter the name only first and present them with a table with input fields after submitting the textarea, with one row for each name that the user entered.
