I don't even know if the cap would be necessary...possibly just the big 3 and a red or yellowtop optima...

In my Pontiac Sunfire, which has a measly 105 amp Alt (I think, don't quote me on that). I was running around 1000 RMS with no noticable headlight flicker, just interior lights, did the big three, and everything was perfect, just had to turn it down at stoplights to keep the voltage up.

I'd say it'd be much cheaper (and more polite to those around you ) to just change your habits while at stand-still.