Might seem obvious, but don’t forget to put your passport or ID card in your hand bag/wallet. You have to go through passport control upon entering the UK by plane, train, car or boat.
Bank cards in the UK
UK bank cards are Visa cards. In most European countries Maestro bank cards are more common. Be aware that you might have problems using a Maestro bank card in shops, restaurants or cash machines. Cash machines at the airport or big (international) train stations usually accept all bank cards. Therefore, take out some cash upon arrival in the UK to ensure you can go shopping immediately! Or exchange some Euros, US Dollars etc for British pounds before you leave of course. (Bear in mind that exchange desks at the airport, train station or hotel often charge high transaction costs and offer a worse exchange rate.)
UK plugs have three pins and are different than European plugs. So, make sure to bring a converter with you so you can charge your phone during your holiday. You could also buy one at the airport or in the UK, but it’s probably cheaper and less stressful to have one before departure already.
Flying: online check-in
Don’t forget to check in online and to print your boarding pass before you leave for the airport. Especially when flying with budget airlines as they charge lots of money to print out your boarding pass at the airport for you.
Do not print double-sided! It’s better for the environment, but not helpful for travelling.
Flying: hand luggage
Different airlines have different rules for sizes and weight of hand luggage. These rules also tend to change and could also have changed between the time you booked your ticket and your departure. Therefore, make sure to check the latest regulations on the website of your airline. If you are flying with a budget airline and you exceed the sizes/weight, you will need to check in your bag in addition to paying a huge fine!
For the moment there is also still a restriction on liquids in your hand luggage. In total you are allowed to carry 1 litre of liquids in your hand luggage, but note that all individual bottles/jars may only hold 100 ml. Put all your liquids in a transparent re-sealable plastic bag (check online what sizes these bags may have).