Hey, I shoot a P09 in Limited and Carry Optics! Good times.

I wear a $25 Midway USA belt and a canvas magazine pouch kind of like this, with the flaps folded behind the belt. (Technically, any permanently-attached retaining devices have to be engaged in USPSA, but that's not likely to be enforced at a club match, and you can snip the flaps off if need be.)

Three magazines is enough. I like to carry at least four, so I have three on the belt and one in the gun.