Please make sure to check that you have a valid passport (United States citizens require a passport valid for at least six months). You do not need a visa to enter Israel.
You are usually allowed one checked piece of luggage on transatlantic flights and one (1) carry-on bag. It is very important to check your airlines regulations as to the weight and size of the bags.
Keep your cash and personal cheques, with you at all times and make sure your credit card company knows you will be travelling to Israel.