Print out all your confirmations: SDCC Merchandise pre-order, Exclusives Lottery wins, tickets to parties, anything that you think you can get on your phone, don't trust it and print it. Some places only accept the print out too.
Make sure you have binoculars, sunscreen, swimsuit, a few pairs of shoes, extra socks and underwear, and business cards if you are handing them out this year. If you are cosplaying make sure you have all the parts for your costume. And most of all, YOUR BADGE!
I was trying to go from memory for packing and I decided that I shouldn't trust that, so I pulled out my travel folder and found a fun checklist from Crazy for Comic Con's 2012 post!! It was perfect, it helped me remember to get the binoculars out and into my carry on. I love to use them when in our hotel room, if we are lucky enough to get a view.
Another fun thing that someone did and I "stole" :) was creating a secret Facebook group with your friends so that you can safely post where you are and when so a potential meet up could happen at any time. Instead of trying to text everyone or Tweet out your info publicly, I though this was a great idea. So I created one for my group of friends and I am hopeful it will work for us. *Crosses fingers and toes for good service in the center*
I also highly recommend using the My Sched that is offered by CCI. If your friends all use it and you are connected by social media then you can see your friend's schedules and see if anything overlaps. My hubby and I even use it for each other!!
Last but not least, have fun, be nice, sleep well and remember we are all here for the same reason... the love of comics and all that entails.