Forget the caps. They are a waste of money in most applications.
If you get a cap, make sure you can take it back when it doesn't help.
Get good cables and use good batteries. I like Optimas but if you want to be able to pound it with the engine off for a long time, you might want to look at Oddesy. There are also extremely large format batteries like 4D that might suit your application.
Do a search in the A/V forum and you'll find tons of battery information.