As an old timer at the Sumit I have gone through several iterations of what I carry in my bag.
I always take a large suitcase. It is half empty on arrival and completely full when I leave. As a chapter leader it is a great opprotunity to gather give-a-ways. You will get a of stuff from vendors and from PASS as well. There is a FedEx at the convention center if you prefer to ship stuff home.
Cables and Batteries
You need cables! USB full,micro and mini depending on your phone/tablet. All your chargers for your fun toys. Batteries for your mouse, pointer or wireless keyboard. I also take it a step futher and pack a rechargeable battery pack so my phone and laptop have a buffer. I always see people glued to a wall outlet all week long and sitting on the floor. Good luck jockeying with a thousand other people for that outlet!
I make sure my laptop is in tip top shape. There are computers available in a pinch but getting time on them can be hard.
I carry a tablet for the bulk of the event and leave the laptop in my room. Lighter and better battery life are the biggest reasons.
Again, do a checkup on your phone! It is your connection to home, friends and work(yuk!). It is also your gateway to all the impromtu events. Find a twitter client and watch the #sqlpass hash tag. Google plus and Facebook are also good sources for info. I also have a GPS car finder app. I tag where I am then go exploring knowing I can always get back. I hope they do a guidebook like they did for SQLRalley. Lastly, I use Skype on my phone and laptop so I can video chat with my three year old son.
Internet can be spotty with a full hotel and full convention center. I carry a Clear 4G puck since there I coverage in Seattle. Most smart phones have a teathering option as ell. Be careful though, it usually costs more and you can burn through your data plan.
I wrote this post using the wordpress app on my phone :-)