Just remember that the only "requirement" is that you can't have anything sent back to your resort the day before you check out. That's because they can't guarantee it'll be there before 11:00. So if you are saving your shopping until your last day, you can't use the delivery option.
But yeah, they deliver anything. A small bag of postcards gets the same treatment as anything else.
Remember to keep your green receipt for claiming the package. And you'll be asked for photo ID as well. All resorts now have you go to the gift shop to pick up the packages. And you don't have to do it that next day, either. You can wait if you had multiple things sent back.