My 'need to haves'
- wrenches as Minnfyer mentioned
- Ball link pliers
- blue Lok-tite (threadlock)
- pitch guage
- side cutters (for cable ties)
- dremel (for cutting off bent flybars )

My 'nice to haves' (often borrowable)
- link duplicator
- bearing greaser
- ball link sizing tool
- some form of headspeed measurement device