How can I improve my car audio system?

I have a '06 impala and im puttin in 2 12" kicker CVX 1500watts each 750 RMS each, rockford fosgate punch amp800.4 for the subs and kicker zx200.2 for mids n highs. i was wonderin should i get a stronger battery a capacitor or the big 3 upgrade, if so what kind and any other suggestions that would be helpful