I would agree with Rich, those front bolts are essential spares; I've not run mine much and have bent 2-3 aleady.
I would also recommend the B5 plastic shock caps and standoffs - and you might need to get a couple of packs as one of mine didn't fit right, regardless of which shock I screwed it onto, it didn't screw all the way on and eventually starts leaking oil. Some folks on rctech have commented the same. They are pretty cheap though so not too much of a hardship. You'll also need to 22-25mm bolts to secure these onto the shock tower. If you mount them screw first, nut at the back, it makes it easy to change position but more crucially, less likely to dig in on a roll and break something. You'll notice that Ty Tessman mounts his shocks using the same method.
CF arm plates again, necessary. Maybe not so much in very low grip but I think the plastic is a bit soft anyway and the CF does make a noticeable difference (for the better IMO).
On the subject of the arms being soft, one of my front ones has either prematurely worn or been pulled out of shape on the inner hingepin. I've contacted HPI (who have been very helpful in the past) but curious to hear if anyone else has experienced this.
I also put an alloy servo horn on as the kit servo saver looked like it would be a liability. As long as you have a strong metal geared servo, should be OK (famous last words)...
I've not tried the option towers yet so cannot comment on those.
HTH
