I always break down my vacations into 2 basic categories: photo vacations and family vacations.
On a photo vacation, I take my digital SLR, several lenses and what always turns out to be 50 pounds of support equipment. These photo vacations revolve around being the right place at the right time to get the sun in the best place for that perfect shot often leaving before sunrise.
The family vacation is based on a very different schedule and the loads of photo gear are replaced by "necessities" for family. I try to get everyone involved in photography and pass out gear based on age, interest and location. For the younger kids I hand out disposable film cameras--preferably ones with a flash built in so they can get great shots even at night. If there is water, dirt or dust involved, they get waterproof disposables which are extremely durable and even float, helping kids take pictures in the water.
For older and more responsible children, I entrust one of them at a time with a point and shoot digital camera. I insist that the wrist strap is used and tightened--this one important detail can save a camera from "death by sidewalk."
I have one daughter that has clamed the video camera as her own. She loves to shoot every activity make a video journal of the trip as she goes by adding personal commentary and voice over descriptions.
As for me, I take a small digital SLR with one lens. Several manufacturers now make great all-in-one lenses that start out wide and go telephoto while still being compact and lightweight. I make sure to have a small case with a waist or neck strap so I can get my hands free and protect my camera.