Right now I don't have a date planned to do a Rim to Rim - I need to find someone to join me. If someone from this forum is going and doesn't mind me tagging along, I'm game - as long as I can work it into my schedule. Personally, I'd prefer to spend a night at the bottom and not try to do it all in a day.
I don't recall there being cold bottled Gatorade at Phantom Ranch, but they do sell electrolyte powder to mix into water. As far as beverages at the Cantina, DO NOT miss the lemonade! I know it sounds silly, but the lemonade at Phantom Ranch is probably the best I've ever had! It is very sweet, so if you're not a fan of drinks full of sugar, it's probably not for you.
Also, there are some neat patches, pins, t-shirts, etc that you can buy ONLY at Phantom Ranch - so maybe reserve some space in your pack to haul a souvenir or two out. If you're really against the extra weight, and don't mind paying a few extra bucks, you can mail stuff home from the post office at Phantom Ranch.