There is a new rule regarding buses and trains in Israel. Everyone must purchase a “Rav Kav” card BEFORE going on a bus/train. The bus drivers will not take any money.
You can purchase these cards at the central bus stations and train stations, as well as at the airport. The best place is to buy them is at the airport at the Transportation counter in the Arrivals Hall (near where the Sar-El groups meet). The cards are 5 shekels and then you put as much money as you want. I would suggest a minimum of 50 or 100 shekels. If you are going to be in Israel for a few weeks and plan to take a few bus/train rides, you should probably put 100 shekels on the card because if you run out, the bus drivers will not add more money once you are on the bus. There are kiosks and stores in the cities where you can “refill” the cards, but NOT on the buses