I can really only give advice for Martinsville, been to other tracks but not often enough to know them well.
For Martinsville:
- Pack a big cooler, and buy an extra seat to have a place for it. Pack the following: Any drinks (soda/beer), bottled water, snacks/lunch. Always pack a little more then you plan on eating/drinking at the track. If you do bring your own beer be aware that if you act drunk in public you will get arrested on the spot.
- If you're going to buy food at the track plan on standing in line for awhile. You will miss a lot of the race if you go very often so plan to get everything in one trip. I suggest the hot dogs which honestly don't taste as good as they used to and aren't anything special but at least you can say you had one!
Don't buy drinks/beer because they are a rip off.
- Don't just show up on Sunday: Spend the weekend. You can watch practice, qualifying, and probably at least 1 or 2 other races going on at the track over the weekend. If you can tour the pits, walk the track, and make sure to chat with people you meet. When I was a kid I got to sit in the cars and a lot of other fun stuff just because the drivers were really cool.
- Don't get a hotel in Martinsville because they jack up the rates when the cup cars come to town. Instead stay in Eden, NC which is only a short drive away. You can get a really cheap room and its a nice area. A lot of the drivers and teams stay there.
- If you can enter the track from the back entrance, less people use it. You might have to park and walk but at least you avoid the huge crowd and traffic jam at the front entrance.
- If you use the front entrance come really early and park your car at one of the locals houses. Unlike a lot of tracks Martinsville has houses located right next to the track and these people will allow you to park for a small fee. You'll be a short walk away and you won't really have to worry about anyone messing with your car. Prices vary but you should be able to park for $10-$20.
- Turn 2 offers the best view of the track imo, turn 1 begin a close second. If you can get seats there about halfway up. You don't want to be too close to the track because something in the infield may block your view of the other side.
- If you value your hearing wear ear plugs.
- Bring something to keep the rain off you...trust me you don't wanna get soaked in the stands. Even a sheet of plastic is better than nothing. You will eventually get caught in the rain at the track...it happens. This is why you pack extra food/drinks so you have something to tide you over.
- Extending on the above: plan to not work on Monday in advance. In case the race does get rained out you can come back on Monday. Monday races are actually pretty nice because they aren't as crowded.
That's really all I have. Hope it was helpful.