You can't go back!
At least, I can't!
Several times I have ended up buying an item from Amazon to ship directly to my daughter at school.
For small items, comparing what it would cost for me to ship something she left home (such as her iPhone charging cord) vs buying a new one from Amazon with free shipping, it becomes a no-brainer, and that doesn't even consider my time to find box, pack, and take to UPS!
I've sent lots of birthday and graduation presents using Amazon as my postal service because they are fast and inexpensive! I can check to see when it gets delivered and follow up with the recipient to make sure everything was in good order!