Differentiate between CF production and CF iron if you could. 
Production means conforming to the USPSA Production rules about type of firearm allowed, very limited modifications, and non-race holsters that are placed behind the hipbone. Also, limited to 10 rounds in the magazine after the start signal.
Limited (used to be Centerfire Irons) is basically any gun you like with pretty much any modification you like in whatever holster you like placed anywhere you like (other than crossdraw) with the exceptions of 1) must be iron sights, and 2) no compensators.
Short form: Production is for folks with Glocks, M&Ps, XDms, etc, that don't have hardly any modifications to them, all in normal-person belt holsters. Irons is for folks who like more expensive tricked-out guns like 2011s in race holsters.
Top-used Production guns:
Here's a fairly standard example of a Limited gun:
There is a also a "single stack" division for those who like shooting 1911s. Similar to Production, guns used in the Single Stack division must conform to USPSA Single Stack division requirements.
You don't need any sort of competitor "rig" (competition belt and mag pouches locked in place) for Steel Challenge---you may see some, but that is just because people are using their normal USPSA rigs. They aren't necessary for SC.
In Steel Challenge, you just need a good holster, on a belt that will hold it in place. (You can carry your magazines in a bag that you set on the table next to where you shoot.) You don't have to have a competition belt, mag pouches, etc---just a gun, a holster that covers the trigger guard and a belt to holds it up, and several magazines.
And ammo.
For some commentary about what equipment you need to bring, there's this:
And for a general overview about Steel Challenge matches at ENGC, there's this:
http://nebraskafirearms.org/forum/index.php/topic,6854.0.html
