I mostly do local short to moderate length hikes here in the mountains of Northern Arizona. I don't have any experience with hiking Colorado's 14ers, or anything similar.
My narrow CamelBak pack allows enough air circulation to keep my back from getting very wet with sweat. I sometimes don't bring the pack, if it is a short enough hike to not to need to bring my lunch. But even then, I usually carry a water bottle or a bottle hanging from a strap over my shoulder instead. In the past, I used to use a fanny pack which carried water bottles on the belt. That worked well too. For overnight backpacking trips, I also have a large older style backpack, which I have had for about 20 years.
I wear a broad rimmed hat and sun screen for sun protection. During the summer, I wear a hat with an open mesh on the sides, which allows the sweat to evaporate. A handkerchief, comes in handy if I start to get sweat in my eyes.
About 10 years ago, on an overnight trip to the bottom of the Grand Canyon, I wore those special hiking pants with zip off legs. The change in altitude creates a surprising difference in temperature between the bottom of the canyon and the rim. I wanted to be able to adjust to the changing temperatures, while avoiding the weight of extra clothes.
On an extra cold windy winter day, I occasionally wear flannel or fleece lined pants and/or long johns to stay warm and comfortable. I occasionally also wear a hat with fold down ear flaps and gloves. Even here in Arizona, it can sometimes get fairly cold at higher elevations.
During the summer time, I have frequently had a clear sky when starting my hike, but have then later found myself in a hard afternoon thunderstorm. I like to bring along a small rain poncho or rain coat, during the summer.
A local ranger station will usually have some free 8 1/2 x 11 inch, letter sized, maps of each individual Forest Service trail. Another alternative would be to buy a good map, or to print out your own custom letter sized map from the TOPO Colorado software (I have the TOPO Arizona software).
If the trail is not very well marked, pay attention and make a mental note of some of the nearby land marks. That way you will be able to roughly retrace your steps if you accidentally get off of the trial. Occasionally, a poorly maintained trail will start splitting in various unmarked directions, making it easy to loose the trail. A map and compass and/or a GPS might be nice if you are on a long trail that is not well marked and not heavily used.
Having a small LED flashlight could help you find your way, if you fail to get back before dark. As it cools off after dark, I could put on one of those supper small jackets that come in a small stuff bag. In colder weather, I would bring a heavier jacket. I doubt that a heavier jacket would fit into my small CamelBak pack. I would be nice if I also had a slightly larger day pack, just for occasional hikes when carrying (but not always wearing) a larger jacket and/or possibly bulkier rain gear, plus my lunch and water too. A space blanket would would take up very little space in my small pack.
A small mirror or a whistle could be used to attract attention, if you are lost or have a broken leg, where there is no cellphone coverage. I sometimes bring along a couple of small individually packaged throw away disinfectant paper towels for cleaning my hands after using the pit toilet, at the trail head. There usually is no water there. Massage oil and a massage for your wife's sore muscles, might be appropriate after you get home.