If you need something like a fan to sleep, I would take one with you. With hotels at maximum capacity, they may not have one available.
You may want to take some pain killers, just in case.
Expect water and drinks to be around $4 a bottle, more if it's alcoholic, so you may want to bring some. Snack bars may be helpful too, especially if you plan to schedule a lot of things back to back. (More on that later.)
I recommend bringing a canvas grocery bag if you intend to shop in the vendor hall (and you should intend to shop in the vendor hall.) Some vendors, like CoolStuffInc, will give these away as well, but better safe than sorry.
There are lots of great restaraunts, but you should check out St. Elmo Steak House. It's pricey (with steaks costing up to $50) but amazing. It's your anniversary, so treat yourself. They will make sure you have a good time.
When it comes time to schedule events in May, leave breathing room. Don't schedule any events back to back, because it can take some time to get from one place to another. Also, there are tons of things you can do without having events scheduled. My first GenCon was three years ago, and I only had one small event scheduled. Dropping into some events do cost money though, and this is done in the form of "generic tickets," which can be purchased at the main convention center entrance for $2 a piece. They are also 80% refundable (in the form of credit) at the end of the convention for any that you don't use.