When travelling through/via an airport in the United Kingdom ensure you have £1 coins with you for the luggage trolleys. You’ll need one per trolley to release the trolley from it’s parking bay where it’s locked to the trolley in front of it. It can be very frustrating unloading your gear from a taxi only to find that you don’t have any coins for a trolley…

Interestingly 1 Euro coins are the same size.