#1 - What strings are you using? I had my first bout of shoulder pain after using poly for about two weeks. It got cut right out immediately. Other than that, ice and ibuprofen (or better yet, Aleve). And, lots of rest. Remember, if you need to, there will be other tournaments. You only have one serving shoulder.
#2 - Water. Water. More water. Gatorade is nothing but sugar. Water. Start the night before (like Dats said), and keep going until well after you're done. Bananas don't really help that much. Stop eating McD's and eat some real food and nourish your body.