After rereading the thread, I would take saddlebag, water bottles, helmet, shoes/everything for the ride down except the bike. Then, make a 2nd trip for the bike. The extra flight of stairs each ride will be benefical for your health. Might even put some more muscle on your legs. Win win.

Edit: It seems we had a similar thread where a guy was carrying his bike down a lot of stairs and wanted to do something about his shoes possibly slipping on the stairs. He didn't want to remove his shoes for the stairs and was asking for suggestions.