Re: Extra parts
The classic answer for most firearms is the extractor, ejector, firing pin and any springs, pins and rivets to install the above.
The scope is another failure point (less so with some of the higher end tactical mounts than lighter weight sporting mounts), including the mount and bases. When go to an out of state shoot have been known to toss in an extra scope and rings (i.e. have an older 1" Leupold for this purpose and testing new guns).
But for a Rem 700 I went with the package deal, another rifle ;-).