Like Ploveking stated, I too, wear cargo shorts. They have pockets big enough to hold the Gencon badge holder if I go out to restaurant at night, my phone, a small camera, wallet in a velcro enclosed pocket for safety. I use one of the rfid metal wallets, works pretty good. I have used various backpacks over the years, the black canvas bag of holding, which was great but it held so much it hurt my shoulder. I always sling it over one shoulder for convenience. The black canvas Gencon messenger bag I tried a couple of times and it works but it has no structure so any papers, small prints could get bent. And then there is this old green Eddie Bauer backpack that I've used for several cons, and year after year, I end up with that backpack because it is so versatile, but last year I bought one of those modular backpacks they were selling by the Entrepreneurial Avenue area of the Dealer Room so I am itchin' to try it out this year. I got the harness system that acts as a mini backpack with it too, which will work great for the Wednesday and Sunday of the con.
Bottom line is, if you have options at home, try them out. Pack different ones with the essentials that you want to carry everyday plus room for items to buy then walk aroud the house for a bit to see what you think, you'll be carrying thios thing 10 hours a day for almost 4 days so a good padded strap is key. Take a small card box for promo cards and such and a small box for other promo items like minis or dice, this should keep you organized and preserve the condiiton of those items, pl;us make them easy to get to.
I must throw my weight behind the Equilibrium modular bags from last year. I haven't used mine as much as I'd like (because I was somewhat fearful of how it would be on planes, though I see others have done it remarkably well).
I was planning on using the base only while on the floor (or a thinner attachment), and then my Duluth Trading (Duluth Flex) cargo shorts to carry everything else (the cargo pockets stretch something fierce when needed). Then, there's also the Duluth Trading vest (kinda like a photographer's vest) that looks like it could carry a ton and breathes pretty well.
On the messenger bag (and discomfort) topic; I learned the the hard way with a heavy DSLR; put it on one shoulder and set the bag on the opposite hip/butt area. This allows the weight to be distributed across the body (though nothing can prevent all soreness).
Do not make the same mistake I made last year and use one of those drawstring sacks (especially with a heavy water bottle); my shoulders hated me on that trip, and it was hard to stay organized.
I use 3 Chrome backpacks of varying sizes ( small satchel, med-large messenger, giant backpack, which doubles as airline luggage). I switch throughout the Con, depending on what I'm doing on a given day.