Before you leave, buy a temporary tag to place on your pet's collar with your friend's address and contact number. A simple luggage tag is a good idea for this.
Make sure that you are contactable in case your pet ends up at a pound. Many cases occur where pets are left with friends and nothing is done by these friends when the pet gets out. If your pet is microchipped make sure your alternative contact details registered with the animal records centre are up to date.