.... Hmm, if you are travelling to places you may never visit again then surely leaving your 'spare' camera back in your hotel in case your 'primary' camera fails can result in missed shots even if your hotel is within a short walk from where you are shooting.
Personally I advocate a 'spare' camera body which is
exactly the same as your 'primary' and which even has your exactly matching customisations loaded (easily done via Olympus Workspace) - Muscle Memory should never be disregarded as unimportant in achieving your goals.
But in my case, I have two identical bodies with me when out shooting - They are both 'primary' although I am aware that if one fails out in the field then I still have the other I can shoot with. If you are wondering why I do this
it's because I'm a poser and it looks cool it's because I view my lenses as 'primary' (not in the prime/zoom sense) and the bodies are just controller units - I don't lose time and miss wildlife shots while swopping between two lenses and there is less risk of internal ingress of debris/rain etc etc.
But of course it depends what kind of photography you do.