This is one of my favorite tips I've ever learned on the DIS!!!! We've done it our past 2 trips. I UPS it down 1 week ahead of our trip. It is always there waitinfg for us. It is usually in the computer when you check in, that you have a package there.
I send down things that won't need to be taken home: suntan lotion, snacks, cereal, sppons , bowls, personal care items in travel sizes, wipes, diapers, pullups, disposible rain ponchos. Our 1st trip I actually made my own welcome baskets for the boys and included those. Well worth the money!!