How to carry OM-D E-M5 to be accessible when backpacking?

I don't know what you are planning but simply around the neck is an option.
Of course it flops around and may interfere with other straps. So the best is to hold it in your hands. When the scenery matches that's the way to go anyway...

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And forget not that the earth delights to feel your bare feet and the winds long to play with your hair. - Kahlil Gibran, The Prophet