to hide an extra set of anything you really need to navigate or operate the boat (excluding an extra engine, sails, and dinghy - I mean even if you had an extra dinghy how could you 'hide' it aboard?).
There must be some nook or cranny of the boat where you could hide a handheld VHF, a handheld GPS (even better, a handheld chartplotter: the Garmin GPSMap 78sc looks good! I've been thinking it might come in handy to have a spare chartplotter and a handheld can run independently of ship's power and be used for dinghy navigation as well), a spare copy of the passport(s) (if you have them), and some extra $. Please note this is not a criticism of anyone.

Jerry