Log on to RCI's website and they have a section of the site to purchase items and I believe you can do it on line. If not, call RCI and they can arrange. Have done this in the past and they have come through every time!.
Friends of ours gave us a "shipboard credit" on our last cruise which pretty much paid for our drinks all week. We really appreciated it. Also, our daughter sent us flowers since it was our 30th anniversary. I really enjoyed the flowers but you have to leave them behind - they won't let you take them off of the ship when you return. They both just called the 800 number to make the arrangements. I hope this helps!