front A-arms
caster block's
i keep at least one full set of bearings spare in case i blow one out. (front and rear)
RPM ball cups
also grab some of the shims that are between your caster block and steering knuckle as they tend to run away when you break a caster block.
for the most part if you lawn dart it, it puts the load on the A arm.
if you hit a pipe you break a caster block.
so far im down like 4 caster blocks and one a arm in about 2 months of racing once or twice a week.