TheBlueKnight,
Some things I've picked up over the years going to Cons of all shapes and sizes:
I suggest doing a few laps around the exhibitor hall before buying anything.
Lap 1, you scan and see what booths you want to focus on.
Lap 2, in depth look at the booths you noted before, picking out things you want to purchase.
Lap 3, go back and buy the march you wanted.
This way, you don't have to lug all your kit and newly purchased goodies as you meander through the hall. I also suggest dropping stuff off at your room, car, or any storage area absolutely absolutely trust, so you can go enjoy panels and the sights without hauling everything with you.
Spare/external battery PLUS charger cables (fat load of good it does you in your hotel room, or worse, back home) are a godsend. My phone's battery is pretty good, but after using it for several hours texting, making phone calls, using the internet, and looking up the floor map, you really can't expect it to last all day, and right as Mark Hamil is two feet from you in the hallway getting up to shenanigans, your phone will be nursing one percent.
Before you even leave home, find yourself a good gel insert for your boots/shoes. Best ten bucks I've ever spent. When I went back to wearing my shoes without them recently, I noticed the difference, and that was just casual walking around, not nearly the mileage a Con always is.
Bring plenty of repair stuffs. My kits broken straps and plates doing the most trivial kit-ups at home. There will be plenty of folks that probably have some, but its always good to have some on-hand too. This will be the first event I'll be kitted up for, and I'm planning on bringing my hot glue gun (to the hotel, not the Con floor), small sewing kit (I'm planning on checking with the Con rules to be sure its ok to bring a sewing needle in, can't assume things like that anymore), extra elastic straps, and extra velcro, not to mention small things of touch-up paint and a brush.
I don't claim to be the most experienced at this stuff, just thought I'd give you the stuff I've gotten over the years with my experience.