My husband and I did the Ocho Rios Original Canopy Tour this past January, and we did not take a backpack or anything with us. They said you have to hold onto your possessions at all times so not sure how it would work bringing along a backpack unless you're planning on wearing it while you zip, I don't think they want you leaving things on the bus/van for security reasons.
I did have a fannypack with my camera, etc. but that was it.
I had bug spray in my fannypack too, and we used it although I'm not sure we needed to as we didn't see/hear any mosquitoes or anything.
DH wore shorts/t-shirt, I wore jeans/t-shirt. Good walking shoes too as you walk in and out of the zip-line area and it can be muddy if they've had rain, and there are steps (downhill going in).
It's an awesome excursion, I hope you enjoy it!!
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