This article is a general compendum of what I have learned as an IDPA shooter, Match Director, and a Safety Officer. I hope that the newbie as well as the old hand will find something useful here.
To shoot IDPA, the rule book states that you will need at the very least a handgun, three magazines or two speed loaders, and two magazine or speedloader pouches. This is quite true. With this equipment you will be able to compete admirably.
There may come a stage like the Classifier or IDPA Quick Skills test, where it will be nice to have four or five spare magazines. It is great to have them preloaded and be able to just grab a third or fourth mag instead of pausing to reload your exhausted mags. The clock is stopped between strings, so there is no time penalty if you need to top off magazines, but I believe that stopping to load magazines can break your focus. Having several magazines will speed up the stage for you and the shooter after you.
IDPA's rules limit the number of magazines to two, so one double or two single magazine pouches will be all you need to play. Revolver shooters can carry three speedloaders (or less. But I also shoot some USPSA and four (or five!) magazine changes may be needed in some unrealistic (but very fun and hard) speed shoots. So if you think you may want to try USPSA you may want 3 or more magazine pouches.
My shooting bag is way too small and sooner or later I'm getting a green dillon one. I was given the bag so I will not complain but believe me when I say, get a big and well padded bag. I did not take my good camera to the IDPA nationals because I did not want to carry a shooters bag and a camera bag. A big range bag would have solved that mess.
It's good to have some extra foam ear plugs and one of those belt hooks that hold your ear muffs. Electronic Ear muffs are the best thing to have but they are very expensive. (and worth it!) Sun screen, band-aids, medical tape, bug spray, and a bag to hold your brass. You should also have, sunglasses, eyeglass wipes, poncho, and a good hat.
I do not have the bucks for a spare gun so I have a parts kit with a full assortment of springs, pins, and parts that are prone to breakage or loss. I missed a match one day when my Cat jumped up onto the kitchen table where my dissembled M1911 was lying. She swatted the recoil plug off the table and it took a long time for me to find it. (It was under the stereo, the only thing I didn't move out of the room) Now I have three recoil plugs. I stay at campgrounds at some events and I figure that if I have a brain fart and launch the recoil plug into the weeds, I had better have a spare.
I also carry a bag with cleaning equipment, spare parts, and some dissembly tools. This is as much to help me as it is any hapless shooter who may need a hand.
Other things that are great to have but not really necessary are a shot timer, chronograph, set of spare leather (I had a galco yaqui slide break at a match) and a spare gun.
Anyone out there who has comments, additions, or deletions; your input is most welcome. Email me