Hi,
In Israel you can use cash, credit cards to buy goods. In fact, using credit card is very common, and they are being received in many places. The question is wether your brand is accepted. They are a lot of ATM machines almost anywhere, so that would not be a problem too. As for change point, it depends. In a bank you should expect to have around 4.68 IL's for a euro plus some surcharge (bankhapoalim.co.il). However, in post offices (postil.com) you will receive a better rate without surcharge. There are a lot of private change points either, but you have to check their rates. If you use an ATM machine, than maybe the surcharge will be less than changing in a bank branch. I would recommend that you change some of your money in the airport by the facilities there (I know there is some BANK HAPOALIM point, and some private change points, or other banks points as well), check the rates. If you are going to central cities maybe you will find better rates there, but you should be aware for the rates. I think that for a start a sum of 1000 IL will be enough for traveling from the airport to your hotel, plus some extras, without paying your hotel bills (where you can use a credit card).
Regards.