Using a shoulder bag instead of a backpack. My shoulder was really sore that year.
Make sure you wear you most comfortable shoes. I bought a new pair of sneakers one year and "saved them" for the con, and it turned out they weren't as comforatable as I thought they'd be.
I think these are kinda related. Whatever bag/shoes/clothes/etc. you plan to use at the convention, test them out ahead of time. If you consider Gen Con a 4-day backpacking trip, no backpacker in their right mind is going to trust brand new gear that they've never broken in, much less tested. Carry around your bag to a few local festivals (containing whatever you plan to have it contain at the convention), wear those shoes for at least a week or two carrying said bag with said contents, and see how everything works out.
Regardless pack a roll of moleskin in case your feet wear in a weird spot you didn't anticipate. You can pick up a roll for somewhere around $10 from Amazon (absolutely saved me last year wearing a pair of boots that I'd thought were long since and well broken in.)
Another thing I've found out is that your load doesn't have to be the same every day. If you have a morning of seminars or something similar and can make it back to the hotel/car before an afternoon of heavy gaming, don't even mess with carrying your bag that morning. Stage your bag the night before and have it ready to grab and go for the afternoon or however your schedule works out.
Finally, as a solo attendee I've sworn off carrying a smartphone, tablet, or anything similar. You'd be amazed how many cool people you can meet having lunch by yourself at the bar in the Ram, hanging out at the beer garden, or waiting in line for an event. Staring down at a screen misses all of those opportunities and, after all, gaming really is a social activity and we're all gamers.