Event Shooting - First Event

Hi guys,
This is my first event.
I am going to do volunteer work (United Way) in an event this saturday morning. I went there today to check the lighting. I don't think I can go more than 1/100 at ISO 400.

This is the gear I want to use in this day
Canon 20D
Sigma 24-70mm 2.8
Speedlite 420EX
2 x 2GB 133x
2 x batteries
WhiBal grey card

Anything else you recommend for this event? like a monopod, 70-200mm, diffuser and comments as well.

inside or outside? that makes a world of difference.

if you are not using a flash, your shutter speed can go as slow as your focal length with little or no camera shake. if your at 28mm, you should be able to get away w/ 1/30th or 1/45th

if your using a flash, you can again get away w/ much slower shutter speeds as the flash will stop any motion - but the higher the ISO setting, the more shadow detail will come out and the more effective your flash will appear (mostly only true indoors)

if its an outside event, you'll need your flash to combat the sun

other stuff for the event:

omni-bounce

flash bracket (a must - i suggest the stroboframe press-t)

spare batteries for the flash - possibly an external battery pack, i use the canon power pack E

business cards

Thanks Mike,
90% of the event is inside.

I'd ditch the monopod, unless they are all holding still. I'd crank up the ISO to about 800 or so if you don't want to use the flash, 400 or so if with flash. I'd consider taking the 70-200 as well.