What do you need for autocrossing....Nothing. Pretty much a car that is in decent mechanical shape (no dripping fluids, battery tie down (oem is fine), a clean interior)
Show up. Some organizations require you to were long sleves. others don't give a shit. I have done it in jeans and a long sleve tshirt at some places, others I have worn gym shorts and a tshirt. If you have a motor cycle helment, bring that. Most be SNELL 95 or newer. Again, check the organzation that you will be racing in qualifiactions. Most places have loarner helments, but I prefer to have my own.
Scca is the big organization for autocrossing. Solo2 is what they call it.
Autocrossing normally isn't at what you would consider a track like Leguna Seca or Road Atlanta. Most of the time, they are in big parking lots or small airport runways. It is a very tight course outlined in cones and may incorperate charteristics of the parking lot into the track, like off camber turns(think of a highbank turn that is sloped the other way causing you to have less normal force). Most autocross speeds are realtivly low, and you may never get into third gear, but it is alot of fun, and will make you a much better driver in the end.
no special licelnses required for autocross
you basicly just need:
a car that will pass saftey inspection (everything tight, battery secured, no parts falling off the car)
working seat belts or harnesses
and a helmet.... the helmet really needs to be be snell 2000 or better... 95 is still good till the end of this year in some places, but if you are buying a new helmet its stupid to get a 95 as it will be no good next year... snell 2005 doesnt come out till around october area... as a general rule all of these helmets will also be DOT approved, but the DOT approval really doesnt mean dick... they want / need to see the Snell approval
also there are different types of helmets and ratings there are M rated helmets (motorcycle) and SA rated helmets (special applications)...
M rated helmets are your basic motorcycle helmets, they are fine for autocross, however if you chose to get more involved with competitive racing they are no good, you will need an SA
SA rated helmets differ slightly from the M helmets... some look vastly different but for now lets focus on the major points... M helmets are pretty much designed to take one big hit... SA helmets are rated for multiple impacts, and also must have a fireproof liner... SA helmets tend to be more expensive than Ms
pay special attention to fit... the helmet should not be so tight it brings on headache, but it should not rattle, either... put it on and shake your head...your skin should travel with the helmet... the idea is that your head does not get a running start before hitting the padding
a tire pressure guage is a really good idea, as well as a tire pump (the little ciggarette lighter ones work fine)
also, stuff like oil, coolant, some basic tools, a jack, some rags / paper towels, window cleaner, etc, will come in handy
something to drink... many events have vendors but not all... you will be out in the sun all day... you will need a few drinks
chairs... it sucks ass sitting in your car all day... standing around all day definatly sucks... you will want to sit... its nice not to have to sit on the ground
if you have a small popup canapy (around 10x10) those things are the shit... shade for the sunny days, shelter for the rainy days... worth their weight in gold
and bring a bag with you to clean up all the shit in your area before you leave... dont leave it there for someone else to deal with!!!!! if there are garbage cans / dumpsters then throw it out there... if not take it with you