Level 1 holster is the norm, I've also got a Soley thumb drive that I' m considering for 3gun(more movement); in Action Rifle I try to keep one hand on my holstered pistol when advancing, just in case.
For carrying stuff in Action Rifle and Tac Rifle I use a "Battle" belt with HSGI Tacos, A double rifle pouch and two rifle/pistol mag pouches; carrying four rifle mags(yay mag laws *spit*) and two pistol for a total of 5 and 3. Extra rifle mags in cargo pockets or my dump pouch, stage dependant. I like that the Tacos are multipurpose, so I can play with my 858 or different pistols.
My suggestion to you(since you asked

), for a multi-use belt system would be investing in a good stiff 1 3/4" width belt (Wilderness 5 stitch) ((max width for IDPA)), and mag pouches of your choice; this could be used in all games. I have the battle belt so I don't have to thread junk onto my belt every time, but it's not that big an inconvenience. Having said all that, many people at Action Rifle run chest rigs, at most you need to do two mag changes on the clock.