In the past I have just bought what is prone to breaking (arms, knuckles,pins).
Another option is to buy another kit.Especially if you are supporting your LHS as I would be willing to bet the store owner would give you a heck of a deal
if you tell him/her you are walking out with two kits under your arms.
You could sell off some of the parts you are not going to use (chassis ect),get some coin back and have plenty of spare parts on hand.
I did this with my 1/8 buggy and it's great to have another set of built shocks and diffs when you are scrambling to make a heat/main.