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

I haven't been on a zip line excursion, so I'll leave that part to someone else, but I can tell you about bug spray. As long as you stay in Cancun proper, there's no danger of malaria, but if you venture out into some of the surrounding areas, as you probably would for zip lining, you need to watch out for the mosquitoes. If you take insect repellent, be sure to get a non-aerosol pump spray. Aerosol cans could explode in a non-pressurized baggage compartment, and they might not allow them in carry-ons. Another possibility to consider is Coppertone Bug & Sun, a sunscreen and insect repellent in one. It saves time because you only need to apply one product instead of two.

I agree, bug spray is good, and possibly sunscreen, depending on how shaded the area is. You can just wear any clothes- that's what we did! It was a blast!