I called the hotel where SMOFCon is being held, and they said that it's okay for me to send a package to myself, and that they don't charge fees for accepting such packages. (Some hotels have taken to charging for this.) I just need to label it with my name and arrival date. So I reckon that next Tuesday needs to be Mailing Day, where I send the box to Oregon and the mailing tube down to Austin.
There appears to be a Post Office that opens at 8:30 AM within a mile of the SMOFCon hotel, and my flight to Columbus doesn't leave Austin until 12:30 PM on Monday, so it looks to me like if I get my act in gear on the Monday of SMOFCon, I could get down to the Post Office and send the tube back to Oregon that morning before going back to the hotel to check out and get over to the airport.