The last tip talked about a rain jacket for you. But it is almost more important to have protection from the rain and other environmental elements for your camera and lens. You can melt and survive but your camera gear will most definitely kick the bucket if water from rain, snow or splashes gets inside the body. Sand can also do a number to your gear. Salt left behind by salt water can corrode camera equipment.
I use a LensCoat RainCoat. Although a little pricey, it is worth every penny. This waterproof yet breathable cover for your camera and lens comes in a variety of sizes depending on the lens size. A variety of patterns are also available depending on your use and preference (black, RealTree, dark gray, digital camo and green camo). The cover fits over the full body and lens, and Velcro closures and cinch straps secure it snugly around your gear. In addition, it has a convenient opening with an arm sleeve for accessing your camera controls.
I have one for each of my camera bodies and long lenses.
But there are some great homemade options as well. A trash bag will work well for keeping your gear dry. Just be sure to keep it tight around the openings (tape would work in this situation on the outside of the bag). A shower cap can also work for smaller camera/lens configurations. Be careful with these options as holes can develop quickly in the plastic.
Another option that can work is to use the leg from an old pair of rain pants. Like the LensCoat RainCoat, the pant leg can be easily slid over your gear and then tape or pieces of Velcro can be used to cinch it down. However, like the trash bag option, be careful about raw elements getting in at the openings on the ends.