Unless you are needing to work on a specific problem with tech support, I would suggest keeping what you carry to a minimum. The days are long and lugging around a laptop can get tiring. depending on where you are staying, dropping it off in your room between the day and evening activities is not always possible.
I've done both, but typically just bring my iPad/tablet these days (I don't have a smart phone), and that's mainly for email, the UC app, and texting when trying to find others. Phones are great for a quick snapshot of a slide, but remember, they usually post all the videos Esri Videos | E360 Videos: GIS, Events, ArcGIS Products & Industries after the conference, and you can get the slides usually from Recent Proceedings
With that said, if you do bring a laptop, they usually have charging stations in the GIS lounge and sometimes scattered around (but don't count on that). If you plan to work on an issue, make sure it is setup so you can access it easily to show the tech. They do have wifi, but connectivity down in the showcase/vendor area is sometimes really slow. They do have computers set up in every product area, so if it is something that can be seen online, or a generic question, they've got you covered. If you want to look at your data, think about loading the fgdb on a thumb drive. Much lighter to carry.
but yes....always good to have pen and paper...and business cards.