After all of your effort carving that expert pumpkin, wouldn't you want it's lifespan to be at least through Halloween? Pumpkins shrivel up after losing moisture so slowing down the dehydration process and deterring the on-set of mold will help make them last longer. You can usually restore them back to their original condition by soaking them in water overnight.

One technique is to coat all cut surfaces of the pumpkin with petroleum jelly immediately after carving. This includes a light coating of the entire inside of the pumpkin. If you can't do the whole inside, at least try to coat the design that you've cut. The petroleum jelly acts as a barrier to seal in the pumpkins internal moisture to help slow down the dehydration process of the pumpkin. You can use a finger to coat the eyes, nose and mouth but you may want to use a paper towel with jelly on it to coat the inside. It's less messy that way. There are also spray pumpkin preserver products out there if you can find them at a craft store.