Just about every airline in the world requires documentation from a veterinarian that your pet is in good health before it can board a flight. Some resorts and hotels may also require the same documentation before allowing your pet to stay there. After all, who wants a rabid dog or a cat with feline distemper spreading disease to other guests' pets?
A veterinarian's checkup should include a general physical examination to check for signs of illness, like coughing or diarrhea. The vet will also make sure your pet's rabies vaccinations and other shots are up to date. You may also get flea and heartworm treatments out of the visit, if your pet isn't already on such medications.
If your pet passes muster, the veterinarian will give you a signed document that attests to your pet's health and vaccinations. Keep this document in a safe place, and be sure not to forget it at home -- it's as bad as leaving your plane ticket behind.
Don't visit the vet too early, however. Most airlines require that your pet's clean bill of health be no more than 10 days old.