Handy Travel 💩
Something I kinda wish I had on the plane to pair my BTR7 to the in-flight entertainment screen. This can also be used so send Bluetooth audio in the other direction so if your car has an AUX jack but no Bluetooth problem solved!
I know other travel esim services exist, but this is the one we settled on and it gave us solid performance with a minimum of mucking about. If you have an iPhone XS/XS Max/XR or newer this will work for you. If you're on Android, look your phone up on GSMArena.com and see if it has eSIM support, even some of the newest ones don't have it (usually the budget ones) so you will need a physical travel SIM
Momax have a bunch of these ranging up to a 170W one for >$200NZD depending on how many things you want to charge at once. The model in this link is the price:perform sweet spot if you bring a dedicated charger for your laptop instead of trying to charge it off the built-in USB ports. You can charge all your other stuff off those. My family used these for ten straight weeks in the UK and Europe and have been using them at home ever since, so that's 9 months of use and abuse with no problems at all.
Easily send, receive, and spend money internationally with no fees or bad exchange rates, all in one app. Even if you don't use Google/Apple Pay, having the physical wise card on hand takes a lot of stress off when it comes to making payments. Doesn't magically make $1NZD = £1GBP though.

Wore these throughout our 2024 eurotrip. They have a decent helping of bass and almost all-day battery. I recommend them if you like mountain biking with music on.
That customs form you have to fill in on the flight back. Yeah, they have an app for that now.
Download your maps to your phone's storage so even if you have no reception you can still navigate.
One app to compare & buy train & bus tickets, get live times across UK & Europe. If you aren't buying a Eurail pass, at least set yourself up with this. It'll save your wallet from getting kerbstomped at the ticket kiosk.
Either this or CityMapper make the job of getting from point A to point B using public transport super-straightforward! CityMapper has a smartwatch app, so if you'd prefer not to get your phone out and risk having it nicked that's a viable option but for us Dunedinites we get access to the Pro teir Transit subscription for free thanks to our local bus company.
Adding this as an alternative to the Transit app. It does pretty much the same thing but you can do it all on your Apple Watch or WearOS watch if you don't want to get your phone out of your pocket and risk it getting nicked (something that never happened to any of us while we were traveling, just saying)