A quality ballhead will also save you headaches. We recommend high-quality ballheads from Acratech and Really Right Stuff. Buy for life!
Bring lots of memory cards and batteries. We'll be shooting a lot! We recommend the SD and CFexpress cards from ProGrade Digital, the fastest on the market
We always bring lots of lens clothes, you never know when you'll need one. You can also choose to bring other accessories, like camera straps.
We work off external hard drives while in the field and use them to back up images. Look for a SSD, as they will be much faster than your traditional HDD drive.
You want two types of jackets - an insulator and a shell. The insulator will keep you warm. The shell will keep you dry. We recommend Arc'teryx and Patagonia.
When we're out for sunrise and sunset, we are at the brink of daylight hours. It's always good to have a headlamp, in case you need some extra light.
On some trips, insects are an issue, like Alaska and our western trips in the mountains. It's a good idea to bring repellent just in case.