Even though flight tickets are electronically stored with the airlines, you should print and bring along you e-ticket numbers and reference codes/numbers. In most cases you will also need them for check-in. The same goes for any kind of travel product which you have booked from home; hotel vouchers, hostel vouchers, car rental/motorhome vouchers and adventure tour vouchers etc.
Make sure to leave copies of all your important travel documents in your e-mail inbox or a portable device such as your mobile phone or a USB memory stick etc. By doing so, you have easy access to re-printing the documents if you should lose them on your way.