Comfy shoes
Great discussion about shoes, and I'm glad to see a couple of people focused on socks as well. Just to add my two cents - if you're going to spend all day on your feet, bringing a second pair of socks to an event is a great idea to consider.
If you don't want to drop the money on a pair of hiking socks, having a second pair allows you to take a few minutes during the day and change socks. It's a tip I encourage my Scouts to follow when hiking. Socks do build up moisture from foot sweat (ick) and a fresh pair will allow your feet to breath more and reduce the chance of blisters. Plus, the time spent changing allows you a moment to check the health of your feet in general. If you have any hotspots, apply moleskin to the area. Cut out a piece double the diameter of the affected area - or even two pieces to layer them - and cut out the center of the piece of moleskin. Put the moleskin on the area so that the hotspot is in the center of the moleskin.
Take care of your feet - and you'll have a better day. Moleskin is too cheap a solution not to have in your bag.
(Always pack moleskin if you're breaking in new pair of shoes on the floor. It's always recommended to break in shoes before spending 10 hours on your feet, but if you're going to do it the hard way then pack some moleskin).