Extra battery is key!Welcome. GoPro's are great for travel.
Accessories... how about a short tripod such as https://gopro.com/en/us/shop/mounts-accessories/shorty/AFTTM-001.html. Maybe an extra battery. How about a suction cup mount to attach to a window to catch a few takeoffs and landings. https://gopro.com/en/us/shop/mounts-accessories/suction-cup/AUCMT-302.html
Similar, non-GoPro accessories can be had for lower costs, too.
And I use this Telesin case https://www.amazon.com/gp/product/B07FF125TZ/ for my 8 to protect the non-replaceable lens when I toss it into a travel bag.
I also really like the Shorty Tripod.