Man thats an open question. On a revo you can remove everything if you wanted lol. But I think what your asking is what can you do to make it stonger lighter and faster. Pretty much what listed before. There are a few that are the big 3 as I like to call them, to remove excess weight and improve performance.
1. FOC
2. Pull start
3. Single stering servo conversion.
If you do those you will have a pretty solid truck that would take alot of beating and keep coming back for more. Then if you want to get into more depth and dig deeper into your pocketts you can do the rpm setup, get rid of the rx/tx boxes, which tekno makes a good lookin replacement. It all depends on how far you want to dig into your wallet and how much time you want to put into your rig.
Bryson