A good pack and a good charger are two important things.
You should probably look into getting some diff shims, some extra diff balls, some Associated Green Slime, Associated Black Grease, an assortment of either Losi or Associated shock oil, and a shock rebuild kit to keep in your pit box. Some pinions and spurs would also be a good idea, so you can track tune or tempurature tune for the best performance in any condition. RRP sells some good sets of billet aluminum pistons, and Kimbrough sells some tough spurs in many different teeth counts and pitches.
Were you thinking about getting anything else?