IT depends on your local track what they require. The local track here DOES reference some kind of National "book" as to times and what is required.
Under 12 sec (for my track) was:
1. Roll bar, single hoop on my Cobra was fine.
2. Nomex "fire" jacket (about $80).
3. Are restraints due to open cockpit (about $30).
Helmet, long pants, shoes are required for everybody. Hey, this is Hawaii. Shorts, flip flops and T-shirts are standard issue. So they actually had to enforce a "dress code" and turn away some drivers every night!
In the 10's? I couldn't run here, requires a full roll cage.