Rob gives excellent advice. The transmission is one of the weak links, and a spare is excellent insurance against trailering the bike home from a tour or missing a sizeable amount of the riding season. Make sure it's in good condition and ready to go.
Final drives rearely have problems, and they're pretty cheap. so it wouldn't be a big deal to sell it. But, on the other hand, a FD doesn't take up much room.
If you're interested in selling some of the extra parts, get in touch. There are a few things I'm watching for.