By "fixed," you mean "rigid" or "non-suspension" frame, not "fixed-gear," right? In that case, it's yes to fenders and rear rack, no to chainguard. Unless you have the bike set up with a single chainring in front, in which case you can have a hockey-stick chainguard. For a chainguard that totally encloses the chain (like the Hebie Chainglider above), you'll need either a single-speed or an internally-geared hub.