The ANKER PowerCore 3 10k:
I had to carry my work Apple laptop with me, and I have a 87W Apple USB-C charger for it. That was more than enough power to charge everything, but I needed the cord ends for the UK and Ireland, and Apple wants $35 for a pack of them. I caught the PlugBug half-off, so it was an easy purchase. If you have an Apple laptop, this is an essential accessory that makes 2 plug-ins into 1.
Amazon link: https://www.amazon.com/Twelve-South-PlugBug-Charger-MacBook/dp/B07GN6Z5KV but sometimes it's cheaper at their site: https://www.twelvesouth.com/products/plugbug-duo
Alternate Choice: If you don't have an Apple charger or a laptop, try out a charger like the KKM USB-C Charger Adapter. It has plenty of charge for an iPad or the PowerCore above, and could slow-charge a turned-off laptop in a pinch. However, it's probably cheap, so you're going to test it well pre-trip.
Alternate 2: Wait until you get there, and buy a 18W to 30W USB charger in an airport shop or a local computer shop, or buy one from Amazon and have it waiting for you at the hotel/hostel.
Wish list: Short Apple Watch chargers
I have a cellular Apple Watch, and I used a lot of battery life on the plane listening to music. I ended up trying to charge my watch using the battery and my long charger cable. That night, I searched these chargers out and ordered one with delayed shipping so it'd be at the house when I got here.
A two pack of Apple Watch chargers at https://www.amazon.com/gp/product/B09BJ9XKHS/ would have been useful. You could plug this into the top of the PowerCore to charge the watch as well, or into the PlugBug to charge the watch overnight.