The biggest thing you need to do before heading to the track is make sure you are financially prepared. There is a saying regarding cars taken to the track, "There are those that have been wrecked and those that are going to be wrecked". Don't take it to the track unless you are financially prepared to push it off a cliff and walk away. You insurance company will most likely not cover it if you put it into a wall or worse yet, somebody else puts you into a wall. Some have even had their insurance dropped for asking their carrier if they cover the car on the track. The other option is to purchase track day insurance. Do some searches on this and you will find some options. Don't be ignorant and think I won't be pushing that hard so I won't wreck. The last laid back track day event I did in the Elise, 4 yes 4 cars blew their engines on the track at different times. If the guy in front of you blows and engine, busts a coolant hose, etc, etc. in a corner you are going to go for an uncontrolled ride. Cross your fingers it is a large grass runoff area in front of you, but what if it is an armco or worse yet, a concrete wall.
Next thing to do is the minimal safety gear. You need more than just a Snell certified helmet, it has to be a Snell SA helmet preferably 2005. A Snell certified motorcycle helmet is not acceptable at some events. SA helmets are "special application" i.e. racing helmets and are designed to take impacts with objects typically found in race cars like roll bars. I would recommend a full face helmet, especially if you are going to run with the top off. Some prefer open face, especially for autocross as they can be a bit more comfortable, but they don't protect you eyes from debris.
The next thing to consider is restraints. Many track day companies will allow you to run with the stock 3 point harness. Doesn't mean it is a good idea, but it comes down to your personal level of acceptable risk. Personally I wouldn't run anything less than a 6 point harness, but I'm self employed so I tend to error on the safe side. Don't be ignorant and ignore the issue. Research the facts, the costs of the equipment, and the costs of the consequences and make a good informed decision on what is acceptable to you.
Head and neck (H&N) restraints are another very good idea. If you decided not to go with a harness, you are extremely limited but there is at least one option. The R3 device is designed to work independently of a harness system. This is the device that I own, although I chose it for its comfort level when I was looking at safe and effective H&N restraints. If you decide to go with a harness, there are many options such as Hans, Defender, etc. Do some research and better yet, find a local dealer and drive the car over there with your helmet and try them on the car. You will find some fit better than others with stock seats. I don't think the Hans will work at all with stock seats so do some searching on here for options.
Fire resistant suit, gloves, socks, and shoes and very uncommon at a track day event. Being production cars, they are much less likely to go up in flames compared to a race car due to mechanical issues other than a wreck, however it has happened. Again it comes down to personal level of acceptable risk. At a minimum, wear 100% cotton long sleeve/long pants clothing. Synthetics are called shrink wrap in a fire and you do not want any part of that. I would buy a pair of racing shoes as an entry level pair just isn't that much money and you need to get driving shoes anyway. I would also throw in a pair of CarbonX or similar socks as most socks are going to be synthetic. Personally I wear a firesuit, but I also own a formula car so I have to wear it anyway.
There are many threads on the technical aspects of prepping the car so I won't get into that. Just do lots of reading and go over the car with a fine tooth comb, primarily suspension fasteners, brakes, and fluids.
