The great thing about IDPA, you don't need much. Gun, holster, (3) mags min, ammo, hearing & eye protection, cover garment.
Depending on what div you shoot, you will need 3mags, one in the gun & two on you belt. A mag pouch, eitehr a double or two singles. Holster is personal pref but must NOT be a competition version. So most use some kind of Kydex OWB or anything IWB works fine. Cover garment can be anything that covers the gun form a vest to your T-shirt. The vest is easy on & off A coat in cold/wet weather works too.
Find out how many stages are being shot. IDPA rules allow only 18rds required max per stage, some can take more if you miss. So plan on 20rds/stage min. & bring a little extra. Go to the IDPA website & look at the rule book. Try to understand the scoring if it matters to you. Go have fun, it's great practice (not training) for anyone serious about their shooting.