Not necessarily what to pack, but if you plan on eating out (which Indy has a number of good restaurants) and are fairly OCD on eating schedule, start eating earlier before you go to acclimate. Plan to eat on the "old person" schedule and you'll generally avoid wait times at restaurants. Also, avoid the chains, they're not only not as good, but the familiarity/name recognition breeds tired gamer impulse dining. 

I agree with trace_sl, get chewable Airborne, they are great. With all of the people walking in close proximity and the hotel rooms, it works. I didn't take it one year, got sick when I got home. I take individual snacks like the 100 calorie Oreo crackers or the Belvita crackers. Healthy and they will hold you over until you can get to a food line somewhere. Water is essential too, take a water bottle for your pack, comfortable shoes, don't matter what kind just so long as you can stay light on your feet. It gets warm in there so shorts and t-shirts are a must. They usually give away some small recycled material handle bags or the messenger bags, grab at least one or two of those for extra carrying capacity. I keep a couple of those small one shot Colgate toothbrushes in my pack, keeps you fresh, and some floss picks too. Don't take everything, I have overpacked for this con many many times over the past 30 years and I never use half of what I bring so make sure it is something you definitely want to use or need. Plan ahead with the Author's Avenue for bringing books to sign. I usually write a list out of everything I need to bring, started that two weeks ago, you always forget at least one thing no matter what.

a list of "Must see, must buy, must bother" vendors.

Oooh, hey a vendor list. I know roughly where the half dozen or so musts are, but it might be a good idea to write them down along with booth numbers.

I have also discovered Jaimesons' Raspberry Lemonade vitamin packets. I am vitamin B12 and D deficient (proven by bloodwork so let's not get on the whole "there's no truth that you need multivitamins and they're all liars" train, shall we?) and I really didn't want to bring whole bottles on the plane (coming from Canada) or buy a multi I would take for five days and throw out before I flew home or feel like a dead sloth because my energy was shot by day two.

These come in conveniently (and more importantly CLEARLY)  labeled individual serving size foil tubes. You mix it with water and drink it. Score! I can throw half a dozen in my luggage and put then through with the medication ziploc. Problem solved.

Some days it's the little things.
 

And i love the lens cleaner idea..  Heck if you can, bring one of those little 'glasses repair/cleaner' kit..  Easy to fit into a pocket..

On the clothing angle, one thing I do, is bring a nit bag (laundry one) so you can toss your used clothes in, so when it comes time to pack up you have your dirty stuff separated from the clean...

Re: using phone - well, the con schedule and maps are available through there, plus Google maps for getting around / finding food

Oh and rulebooks. I can store all I need on the phone rather than lugging them with me.

And friends, nobody uses frs radios anymore, they just text/message/call now.

Some people use dice rollers.

I also have my what to get spreadsheets. And look up if product in dealers hall is decent price or rip off

My main suggestions that most people don't suggest are scissors, tape, and at least one, if not several, extension cords/power strips for the room.

Hotels are getting better generally about having power outlets next to the bed for you phone, but it's not a guarantee.  And onsite, I have to plug in, my phone, my computer, my camera, a back up phone battery, my fit bit, my pebble, and several other things.  You need a power strip.

I travel light when it comes to electronics (Apple Watch, iPhone, iPad, GoPro Hero 4) but as all of them use USB I find the 4-port iClever USB self-contained little brick to be all I need. They have a 6-port unit too...all 2.1 amp ports, as well. 

Yes, they do. 40w 8amp all in a compact little self-contained plastic box :)

Okay, here is one that I never see on the list but that people from my group swear by.

Glide.  

Glide looks like a deodorant stick and is sold at sporting good stores.  You out it on your feet or on your thighs were your legs rub together when you walk.  It does exactly what you think it might, let's you glide all day long with no chafing on your skin.  Runners use it.  All I can say is that it works!  Couple of the guys in my group are pretty husky and they say it is a game changer for Gen Con and all the walking we do.  Your feet, thighs and any other body part you can think will thank you.

Oh...and please folks, wear deodorant!

Food/drink

As I rarely drink sodas, so I bring a pack of cold brew iced tea bags, which I just drop in a water bottle in the am; By the time I reach my destination, I usually have iced tea. I'm just as happy with water, and the day that I arrive ( Tuesday), I will be grabbing a case of water bottles at CVS, as well as a few choice root beers,etc @ that awesome Bottle Rocket store on the monument circle.

Snacks

Before I leave home ( San Francisco), I stop by Trader Joe's.
I'm grabbing a couple bags f turkey jerkey, trail mix, dried fruit, crackers, and a bin or two of dark chocolate covered nuts/fruit. I might bring a small bag of apples and/or oranges as well.
I take advantage of Southwest's 2 free bag policy ( They will be full of awesome loot on the way home). Also, I bring a bottle of hot sauce... Even the blandest chicken sammich ins 1000% better with the right sauce.

Meds

My asthma inhaler, Gout pills, ibuprofen, pepto-tables, multi-vitamins, small sunscreen ( It's not my native Az, but arms, and forehead can get toasted, especially when walking around outside for extended periods).

Personal

I'm there for 7 days, so I bring 8 days worth of clothes, plus 2-3 pair extra socks.bathing trucks...pool time!
Toothbrush,razor,toothpaste,etc... I also bring my own pillow case, as ... Hotels,yuck.
as well, I will prob re-dye my hair this weekend, and I don't want to get blue dye everywhere.

Nerdy Stuff

iPad, new super porta-battery for it and my iphone. 
Rulebooks for Fantasy Age, D&D 5th, The One Ring.
My bag of 50 dice or so, plus various tokens.
pack of ArcKnight gaming mats, about 100 prepaint minis ( Much lighter than hauling my painted stuff),
pens, misc... 

It's late, and I can't even remember if this was a 'What do you bring?' Thread...haha.

-Uriel