Use a seethrough plastic bag (use at least 3-4 layers) (make a whole on the zoom area of the camera) and it should be fine!
if you use a single layer its very likely water will still get trough it...
its very slippy also if yu use a plastic bag so watch out! tbh, my camera comes with the special case for these conditions, but mine is a digital one and has not movable zoom! i am not sure you can get anything to protect the zoom! i'd be very intrested if you find something too
About two or three quart-sized food storage bags should give good water protection. A Seal Pak is a fanny pack that is very water resistant. If you're willing to get a new camera, Pentax makes some that are immersible to a few feet. There is the IQ Zoom 105WR (film) and the OptioWP 5 (digital). You want to avoid changing film in the rain, so start with a fresh roll of 36. If you don't want to carry an umbrella, a hat with a wide brim or long bill can help shield the camera when you're taking the picture in the rain.
There are waterproof cases for many models of digital camera, although they are bulky and can be expensive. The dedicated case for my Olympus Camedia 5050 cost about $180.