First, Diapers.com. If you have never used this site or one of its co-sites (Soap for essentials, Wag for pets, Vine for natural products, they are all awesome and you can pretty much get everything you could ever need), you should try it. They have every baby essential that you need, plus toys, gear, clothes, everything. Best part is, free shipping usually in two days. Before a trip, I order everything I will need for our destination and have it delivered the day before. If we are staying at a hotel, I simply give them the heads up that it will be arriving.
Second, is Traveling Baby. This service can be found in most major cities and allows you to rent baby equipment for your trip. It can be delivered or picked up, and in some cities they will meet you at the airport. They carry everything from cribs to toys to high chairs. It is all sanitized and clean and ready for use. They simply pick it up at the end of your trip.
What services have you used for trips to make traveling with kids easier? This family friendly vacation rental company looks fab, Kid & Coe. Would love to try it sometime.
PS: I have no shame in that this is my son's set up to get through a four hour flight.