As above. Also:
Provide Advanced Passenger information (passport details) to airline.
Photocopy of all your passengers passport identification pages, in case of loss or damage, so that you can get a replacement.
With booking/selecting your seats, you may need to print out your own boarding passes for each passenger.
Currency and other payment options. We have a pre-loaded cash card to pay in shops and restaurants and can also withdraw cash from ATM. Not linked to bank account. DH has a Halifax Clarity credit card for holiday use as you can specify the credit limit, it's not linked to any other account, and is insured against theft or fraud.
In addition to leaving key with someone, will they also put out your wheelie bins/wheel them back, water plants/hanging baskets, make sure you have at least fresh milk/bread on return?
I usually have the cattery money ready at home before we go away, one less thing to worry about.