The company that really specializes in this is Sun Precautions. They sell a long-sleeve Safari Shirt for $80 (www.sunprecautions.com); it has a sun protection factor of 30 and comes complete with a mesh panel in the back for extra ventilation. Very light, breathable material, with sleeves that easily roll up for when you're in the shade. You can pair it with a pretty stylin' Solumbra Sun Hat ($49) and go a long way toward deflecting the sun's rays (the thought of that much sun is making me misty-eyed as I near a long, gray Pacific Northwest winter).
I wouldn't worry much about special shortsmost are made of material that will block lots of sun, and your legs would be exposed, anyway. Pants might be a good choice, perhaps something in the convertible arena such as Ex Officio's Amphi Pants ($59; www.exofficio.com), which have a lower leg portion that zips off. The light nylon material is also fairly cool and will dry quickly.
Your kayaking adventures will pose a challenge because of the sun glare off the water. So be sure you have a good hat like the Sun Hat, or one with an extra Foreign Legion-style neck flap, such as the Outdoor Research Sahara Cap ($37; www.orgear.com). Supplement this setup with a simple bandana over the face and nose, plus of course, some waterproof sunblock on any remaining exposed skin.
And curse you for going to the tropics...