Been out there twice, you’re in for such a treat. It’s a pure golf playground.
Member gifts are so personal and subjective, depends a lot on the member and how well you know them. Can range from a handwritten note, drinks or dinner while there, to a nice bottle of whiskey or whatever they might like.
Caddies: I’ve been out there twice, and no one in our group took caddies. They were available to us, but we all chose to push or carry. Probably pretty dependent on what your member prefers to do, I’d just follow their lead. Normal tip for a caddy should be in the $60-100 range on top of normal caddy fees.
Recs for while on property:
Make sure you get on the mulligan course at least once, and more if possible. The big course is a beast, and 36 a day will take a lot out of you, especially if it’s windy. This is where the mulligan course is perfect. I might actually have more fun playing the mulligan course than the main course, which is saying a lot. Some of the craziest greens you’ll ever see. On one trip, we played it twice, first time with a half set and 2nd as a one club (plus putter) challenge. I can’t say enough about the fun of that course.
The 18 hole putting green is a ton of fun too. We went out after dinner around 11PM and had some putting competitions under the moonlight. Crazy slopes in that green, just a ton of fun to go out there and mess around during free time.
Food: The food out there is really good, and perfect for the course and what you’ll need. Don’t think you can go wrong on the menu, but if there is a must have, it’s the f’n milkshakes.
Others here will have more/better tips, but that’s my recommendation based on my 2 trips out there.
Edit to add: don’t really think about this place as an “ultra exclusive club”. Both times I’ve been out there, it’s as laid back as you’d hope. It’s a pure golf playground for people who love golf, it’s not there to be a stuffy country club, so don’t be intimidated by it or feel like you’re walking on eggshells. Follow your host’s lead for things like hats and cell phones indoors, but otherwise, just relax and enjoy it. It’s a golf club in the middle of nowhere eastern Colorado - people go out there to relax and unwind, there’s no pretentiousness that I’ve seen.