Yep, if a high-output alternator is available for your car, and you
can stomach the price, that's the best way to go.  Without knowing
what you're planning on powering, I can't say whether or not a 200-amp
alternator would be overkill, though.

A second battery will just increase your engine-off playing time, and
the only thing I use capacitors for is when I have flickering
headlamps or dash lamps during bass transients, AND the alternator is
providing enough current to keep the battery from discharging over
time.  If your alternator is so low-capacity that your battery is
discharging over time even with the engine running, no amount of
capacitance or extra batteries is going to help you.

Scott Gardner