For lens, it depends on your needs really. What are you trying to capture and what you felt lacking with current lens to take the pics you have in mind.
For example, at shows/meets, you felt that you can't frame the whole car as space are limited, hence you had chopped the front or rear of the car. Then you'll probably need a wide angle lens.
If you want a nice blur background, you'll need a lens with small F, but the smaller you go, the more ££ you will be paying.
If you find yourself zooming a lot and sometimes feel you need a little bit more zoom, then go for something bigger. Canon 24-105mm seems to be a good choice. (I might be wrong as I'm a Nikon user)
Tripod wise, I brought a cheapo from Amazon for less than £30 to start with. It was pretty lightweight as it wasn't top quality but does the job. Light enough for me to carry around. If you like having a tripod then you can start saving up for a better one.
For flash, again get something cheap to start. I would recommend getting a diffuser as direct flash sometimes over expose your pics so a diffuser will always help. It's just a simple white transparent cover.