Monzo – This card has several key benefits whilst travelling, you can use it wherever you want. Use the contactless feature at partaking stores, withdraw money using the best conversion possible, send your mate money for the taxi he/she paid for the night before. Let’s say that you’ve just paid for a meal in a german restaurant, you will get a notification with how many euros that just cost with the GBP equivalent next to it.
Also, make sure you have downloaded Uber. Getting a regular taxi can be a pain, in my experience prices can be plucked out of thin air by a driver, and the confusion with new currencies etc can be taken advantage of, it also relieves the pressure when explaining your destination. Some cities may not have Uber so check before you go and familiarise yourself with your destination and how far it is etc to limit any opportunistic behaviour.
Tripadvisor – The Pokédex of travel, when you have time restrictions on your trip. Maybe you have two days in Vienna, you want to know that the attractions you are going to see fit with your budget, time schedule and even gather other people’s opinions to justify seeing that over something else in the city. You can also search for recommended hotels and look at reviews for any your planning to stay in. My most important use of this app is looking for restaurants and nightlife, there’s nothing worse than going to a rubbish restaurant.