I found the answer to your question in the following resource:
To purchase items from Wish List:
1. From the iTunes Store homepage, click My Wish List located under Quick Links.
2. Locate the item you want to buy in Wish List.
Tip: To make sure a song or video is the one you want to purchase, you can view or listen to a 30-second preview of that item.
3. Click Buy.
To purchase all of the items in your Wish List, click Buy All*.
Important: All sales are final. You cannot cancel a purchase after you click Buy.
*Buy All is not available in the Canada iTunes Store.