Going to cancun. whats the best thing to wear for zip line excursions? do we need to take bug spray?

I recommend just wearing shorts and a t-shirt. It wouldn't hurt to take some bug repellent. You won't be able to get the aerosol ones on a plane so you'll have to find some other kind, but if not all the hotels/resorts have gift shops that sell things like that so you can just buy it when you arrive. Good luck and have fun!!!