I spent most of my life living - and flying - in the middle of the country. It's hard to find places between the Rockies and the east coast where you can't find civilization in a reasonable number of miles. Heck, keep ten thousand feet of air between you and the earth, and you'll almost always be able to reach a runway! But the west is different.
Flying between the Reno (NV) area and Yakima (WA), level at 10.5K, I looked out and realized that there was nothing but the wilds of central Oregon for as far as I could see - and with western visibilities, I could see a LONG way. It's magnificent, and frankly, there are lots of places to safely put an airplane down if the oil pressure went away, or a fuel line got blocked... but after you find a smooth patch of desert, a lakebed, or a dirt road, and all the pieces stop moving - what then? Do you have a plan? Are you equipped?
Flying along in shorts and a T-shirt are great when your longest walk for help is a few miles. But out here, you could be fifty , or eighty miles (or more) from help. And those who study out-in-the-boonies landings are adamant that "if you're not wearing it, you don't have it." So when I fly this kind of cross-country, I wear a vest with various elements of survival gear - the most important being a small GPS-Enabled PLB. There are thousands of different lists you can find on the internet for everything else you might want in your pockets - but getting found is the big one.
In the winter - I throw in cold-weather gear. In the summer, well, it can STILL get cold at night, so cool-weather gear isn't a bad idea. Sun protection - always. And don't forget water. If you've got that PLB, and you've registered it, food shouldn't be necessary, except to keep you busy until the cavalry arrives.
It's a big world out here, and "walking out" can mean a week's worth of hiking. Fly equipped so that if a bad day happens, you don't have to think about survival - you can just fly the airplane to a good safe landing, knowing that once you're stopped - you got this.