I usually upgrade my stuff when I get a new car.
1st car: radio shack HU, kicker prefab ported box with 2 12's and horns, us acoustics amp, 2 way coaxials (polk ex 4x6 and poneer 6 x9).
2nd car: Panasonic HU, BA Rally components front and rear, single 12" RF Punch ported through rear deck...