TL;DR at bottom.
A few months ago I was at an airport for a transit and tried to connect to WiFi. There weren't any free WiFi hotspots available, only hotspots were you need to pay for. Since I had to check something really important, I chose to pay for the WiFi connection. The payment options were MasterCard and VISA cards. Unfortunately I didn't remember my CVC code. The bunq app cannot be opened without a internet connection so I was unable to check my card details in the app. Since I couldn't pay for the WiFi connection I also couldn't whitlist (forgot) the particular country of this airport so buying something with my card was a no-no.
Also, when I tried to check-in for my return flight at the airport the staff asked me to show them the card that I used to pay for my flight ticket. I have flown more than 200 times but never experienced that they wanted to see my card upon checkin. The particular bunq card which was used to pay for this flight was at my wife's house, so there was no way I could have showed them this card at that moment.
After having a big argument with the manager they agreed that I showed them my card in the bunq app. But unfortunately no WiFi hotspots available so couldn't open the bunq app to show them my card. They couldn't check me in without my card number and verify that the card was on my name. I had already informed my wife to go home ASAP to take a pic of my card.
In the end my wife was able to send a pic of my card with literally a few seconds to spare before missing my flight. I was lucky I only had carry-on baggage otherwise I would have definitely missed my flight.
Yes, I know I could have all prevent this by simply taking a pic of my card and write down the CVC-code somewhere in my phone but I personally think an offline modus to show esstential info about your card at any time would be a better choice.
TL;DR: Phone was offline, didnt know CVC / card number. Want offline modus with essential card details.