1. Jeans-Don't get them too tight because you'll want to be able to lift your leg up to the stirrup without ripping your pants (Note for teens, especially).
2. Layers of shirts/tops/jacket/coat-Be prepared to adjust to Colorado warm days and cool evenings. Also be aware that the Colorado sun can bake your skin, so you'll want light long-sleeve shirts.
3. Cowboy boots-Go comfortable and slip-on (as opposed to lace-ups if possible); Most ranches will have boot barns where you can borrow or rent for the week.
4. Hat-Make sure you're prepared for wind. See if you can attach a "stampede string" that fits under your chin to keep your hat on if the wind is blowing. You can use leather, string, etc. to make one. Western stores and some ranch supply stores will sell them. If you plan on wearing a helmet, check with your ranch's helmet policy and determine if you'll need to bring your own.
5. Camera-There's not a dude ranch in the country that has bad scenery. Get ready to snap those photos! When you ride, it's easier to have smaller cameras. You won't want to trot or lope with a big camera strapped around your neck. And, check with your ranch to verify that they allow cameras on the trail and what the rules are for carrying them. Some allow picture-taking when you stop your horse, some make you get off to take photos, and some allow you to snap noiseless photos as you walk along the trail.
6. Tall Socks-Boots hurt badly with ankle socks. Find good tall socks that don't slip down (See our blog on how to buy boots for specific recommendations on boots and socks)
7. Rain jacket-You're welcome to bring your own rain jacket or most ranches provide these. For the horses' sakes, make sure your jacket is heavy enough that it won't flap too much in the wind. And, a 3/4 or full-length jacket is ideal to keep the rain off your legs.
8. Water bottle-Check to see whether your ranch has a way for you to carry water on the trail. At high altitudes, you'll need to start hydrating well before you come to the ranch and carry on the habit during your stay to avoid headaches.