An essential part of any kit. The body comes with a battery, but you'll want a spare when your primary dies in the middle of an event...it's inevitable. You may also look at some of the off-brand NB-2LH XTi-compatible batteries... there are many cheaper versions out there (try eBay), many of which have battery capacities (this is rated to 720mAH).

A good mid-range flash, enough said.

A sturdy tripod is the best friend of any photographer. Moreover, this one also moves very smoothly, which is great for telephoto photography.

Small but VERY versatile camera backpack. Advertised as able to hold 2 bodies and 4 lenses, but it's actually able to hold well more than that. Basically, this has plenty of room for pretty much anything (within reason) that you may need.

I'm of the persuasion that no good lens should be used without a hood to match, in spite of the fact that you're having to pay $30-$40 for a piece of plastic. This lens hood matches up with your 70-300mm telephoto zoom lens.

A very useful filter which will darken your exposure by 3 stops, though perhaps the least necessary of the 4 filters I have here (likely one of my last purchases) This filter matches up with your 70-300mm telephoto zoom lens and also the 100mm macro lens. It can be held in the fourth pocket in the filter wallet included in the (above) filter kit.

A lens hood for the 100mm macro lens. **This one may be unnecessary, as the lens hood for the telephoto might fit this lens as well... I'm going to test that before I buy this one.

Again, filters for you to learn with. Of particular use with this lens would be the polarizer to eliminate such things as water reflectance. These filters match up with your 17-40mm wide-angle lens.

Perfect standard-range zoom lens for everyday use, one that you can comfortably use as your "go-to" lens. Gives good quality photos, with the USM and Image Stabilization as very nice features. Very good value for the cost.

These filters match up with your 28-135mm standard lens.