Hey, I'm jealous, just thought I'd get that out of the way first off.
A couple years ago I did a three day hike w/45 lb pack down South Kaibab trail to Phantom Ranch, mucked about down there for a couple nights, then up Bright Angel, with an overnight at Indian Garden and a quick evening stroll out to Plateau Point. The best views of the canyon are from within, no doubt about it.
Be aware of your light, as the sandstone walls really come to life as the sun gets low, but if you are a day hiker you should be on your way back out well before sunset.
Plan on some strenuous hikes to test your fitness (have you had a stress test lately?) Wear light synthetic clothing with perhaps a microfibre undershirt and carry a light jacket capable of blocking wind (it can get windy in there.) Spare pair of laces and socks, maybe some moleskin if you tend to blister. Silk sock linings are supposed to help in that deparment, REI should be able to set you up well. Hiking poles should be considered a must, they help take some of the load off your knees and ankles and distribute some to your upper body, get accustomed to using them correctly. If you turn a corner into a strong wind they may save your life (did I mention it can get windy down there?)
Spare battery and as much memory as you have should be taken along, take LOTS of pictures, it's the one you didn't take which was the most rewarding ;-)
A side trip, driving out to Desert View before sunset I highly recommend. October should be clear of much of the haze from San Diego/Los Angeles granting visibility for great distances.
My trek into the canyon was with a Nikon D70s, which is a fairly old camera, but did some great work in RAW mode (honestly take all your shots in RAW you can convert to jpegs at home) and throughout the daylight hours some areas were well lit and others in captivating shadows. It's a magical place.
Enjoy your hike!
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Deja Foobar - A feeling of having made the same mistake before.