Julie, you've gotten some excellent advice on this thread, so I'll just throw a couple of thoughts in:
Food - for munchies on the trail, I've found that taking along one of Doug's monster pancakes, sectioned and stored in baggies, worked great. Complex carbs for sustained energy and easy to chew at altitude (amazing how much of a chore chewing can be up high). Oh yeah - they're pretty damn tasty too!
Ditto the advice on a warmer bag. If you should push on to Trail Camp, you should really have a 20-degree bag. A 40-degree might get you by at Outpost in September (and it might not), but it can get chilly cold at Trail Camp.
Pace, pace , pace - especially with the weight you'll be carrying day one. Keep your breaks on the trail relatively short (10-15 min), and try to get away from the Portal as early as possible. The afternoon sun in the canyon can be a real strength-sapper, especially once you're above timberline and there's no shade to speak of.
Have a blast and be sure to post a TR with lots of photos!