Other than Spock’s sixth finger in that one episode.
(which I can’t find on-line. But I have it in Starlog. Somewhere.)
I’ma stop you there. TODAY’S military electronic equipment no doubt also has surge protectors, and TODAY’S military planes have seat belts. TODAY’S military has never been a good guide for what happens in Trek.
As would anything but bare skin, I imagine. Note the space hippies were burned on their feet, not everywhere. Except the busker who was wearing those fetching thigh-high boots and has to actually eat something to die.
It was the 2300’s. People still had standards.
Nitpick (hey, this IS the Straight Dope). TOS was sert 2265-2268. 23rd century, 2200’s. 
It was those commies of the 24th century that wore long underwear for uniforms.
I just meant in terms of technological progress in garments.
And that’s what I’m talking about; I’m sure in the 1960s and 1980s, the writers weren’t geeking out about the properties of 23rd century textiles and their utility as shipboard uniforms.
But it would explain why the uniforms aboard ship are long sleeved and long-pantsed.
But that’s my point - Trek society clearly isn’t a straight progression from our society in all aspects. They apparently descended to some Dark Ages first. Along with basic Health&Safety standards, maybe they also lost the idea of having uniforms do more than cover skin in WWIII or the Eugenics wars.
A lot of the incongruities of Star Trek are just consequences of having a franchise span nearly 60 years in real life, and about 100-ish in-world.
I mean, today’s cell phones are more capable than the communicators in the first show, and most of the space-agey touch screen stuff and voice recognition in ST:TNG has been surpassed by today’s consumer technology.
But the writers from the 1960s through the 1990s couldn’t have been expected to predict that, nor could they have predicted that the cold war would fizzle out like it did either.
I’m not buying the idea of Trek as an alternate universe; it’s supposed to be a future show based on today. It’s just that 54 years ago, today WAS the future, so they did their best. They’ve already retconned a bunch of stuff- originally the Eugenics Wars were supposed to have ended some 24 years ago, and a whole bunch of other stuff that seems to not have happened.
I’m just thinking the uniforms are writer’s oversight, or possibly the result of some kind of mandate to not have episodes/stories revolve around something so mundane.
See I disagree with that comment. As today’s cell phones only works b/c of the all the wifi towers that’s constructed around the world, and you still can’t call someone in space. While communicators can work on any planets without needing wifi towers, and it can reach a ship in orbit.
The reason for that is the unseen elderly couple in life support who keep arguing about where to set the thermostat for the ship.
My point was that it takes a lot of infrastructure to make our cell phone work. But not in Star Trek.