Hmmmm; completely depends on usage and keeping it to only three is a huge challenge IMO.
...but here goes:
- 1) tires: D606 and MT21 for me
- 2) pegs: Knightdesigns drop pegs
- 3) skidplate: JNS or Ricochet
Personally, I'd also consider bars and handguards a necessity and I wouldn't want to live without my Cogent suspension and 320mm/SV front brake upgrade (easily the two most functional upgrades by an entire order of magnitude.)
I could live without the other stuff I've done though the KLX kit is cheap and the airbox mods, T mod and safety switch bypasses were free...