I started with a cheap helmet I bought trackside from a vendor at a PCA event... that was my first and only accessory at the time... with each year, inevitably I'm accumulating gear... I still prefer to drive without gloves, and for 20-30 min DE sessions, it's fine for most folks. I wear Piloti shoes and really like the way they fit. In fact, I often used them as casual daily or walking shoes. At the DE and TT level, clubs I run with do not require fire suit so I go with jeans or cargo pants w/ elastic ankles and casual shirt.
I upgraded last year to a better helmet... worth the money! pricey, but much lighter, good ventilation and visibility. Here's the model I use
HJCHX10 Auto Racing Carbon Helmet-SafeRacer I also recommend saferacer
I usually run with a fire extinguisher mounted passenger side, but haven't mounted one to the Z yet
I have a huge plastic bin I take with me, full of various spare parts, tape, logs, tire gauge, tire pyrometer, hat, etc. Also bring folding chair.
Just purchased traqmate + chasecam setup, that could be considered an accessory. Not much testing time yet, but I have used it and the software is a snap... RECOMMENDED. previously was using robic stopwatch and/or buddy on side of track
I have an air canister and hoses, but I usually just bring my bike pump for tires ! I get a lot of looks but it works nearly as fast with less crap to haul around !