As kind of a part 2 of "tuning the driver", here is something that I work on personally. Going to the gym, cleaning up what you eat and staying hydrated.
While being fit and strong has realistically nothing to do with RC racing, it can help a lot with your mental focus and reaction times. Being in the gym and working out properly requires a ton of focus. Every rep, every time you push yourself to go a little farther, it takes focus and discipline. The more you can dial in those two attributes, the more you will use it just about everything in life.
With racing, there are a ton of distractions, announcer calling your name or talking about you, background noise, people yelling, trains, cars, etc, the list goes on. so If you can work to be so focused on what you are doing, it will automatically drain out the other things around you.
For me personally, I like to train my body and stay active as much as possible. My genes are not super great and I have some hereditary issues I could face in the future. I like to work all my muscles in the gym as much as possible. I also like to do planks and push ups and throughout the day. Both of these are good for mental strength and obviously they benefit your core strength as an added bonus.
One of the things that I do more often is laps on the ol' KLX110. It gets the heart pumping, its fun and its a whole body work out while I try to navigate consistent laps through the sand we have out here. Another good exercise plan is to get on the MTB program. Climbing with a mountain bike takes focus and determination. I don't know how many times Brent Thielke has coached me up a hill that I didn't think I could do. Then once at the top when you're gasping for air, you realize you can and then like BT says, it doesn't get easier, you just get stronger.
Water is something that seems difficult to drink enough of but, when you start exercising, riding or working out, it makes it easier as your body craves it. For me on a regular basis, I try to drink 120oz. of water and elevate that as needed.
All in all, fitness does not have a real physical advantage in RC but, it can help you mentally and feel more confident when heading to a race. This can also improve your overall living as well and if it doesn't, well at least you have built some healthier habits and should be seeing results. Always aim to be the best version of yourself!
Here is link to some things to help improve your reaction time: