From the folks at Botanical Interest Seeds:
Before carving, wash your hands well with warm soap and water or a disinfecting hand sanitizer, and make sure your carving tools are clean to avoid transferring bacteria to the pumpkin. You may also want to wipe the outside of the pumpkin down with bleach before making the first cut.
Once carved, you can keep your pumpkin perky for up to a week by wiping the inside and cut areas with bleach, spraying with a household cleaning spray that includes bleach, or spraying with one of the pumpkin sprays available in craft or party stores. Then, give those areas a thin coating of petroleum jelly like Vaseline. (Some people use vegetable oil, but it's more flammable---a consideration when using candles.)
Carved pumpkins rot the fastest in warm weather. Keep them out of direct sunlight and move them into a garage, cool basement, or a refrigerator when temperatures exceed 70 degrees. If your climate is humid or it is rainy, you should dry off and refrigerate your carved pumpkins at night. Freezing temperatures also speed decay, so move them to a protected location when temperatures outside are below freezing.
If a pumpkin starts to shrivel or gets a little mold prematurely, you can soak it for a couple of hours in a bucket of water to revive it. (Add 2 teaspoons of bleach for every gallon of water for disinfecting.)
If you are lighting up a pumpkin for more than one night, use a battery-operated candle or small flashlight inside instead of a candle (always safer anyway!). This will prevent soot and heat damage that could shorten the pumpkin's lifespan.
Check out a great variety of vegetable and flower seeds by Botanical Interests--many of them organic--here at Skillin's!