Also ask for the "I'm Celebrating" Buttons. I celebrated my 16th at the Grand with family and friends. We brought snacks from home such as chips, fruit, drinks (also had access to Concierge...we had a lot of food lol). I made party favors for my guests. I celebrated another mile stone birthday there were I had a specific them of Princesses. So I had posters made of 6 Disney princesses (with the names of my guests printed on them as a Party favor) and decorated the room with them and streamers. Also, had homemade goodie bags.
Make sure to note on the reservation that you are celebrating a birthday for your occasion! For mine, we got upgraded to Downtown Disney view for the second celebration (doesn't seem like much but we received a huuuge discount on 2 standard rooms so we weren't expecting much of a view) it's not guaranteed but it was a nice surprise of pixie dust and I received an autographed MM pic along with a Bday wish by phone!
Have fun!!!