In my experience...not a lot.
I have eight brothers. I was one of those girls who had mostly male friends until college. I lived with two guys for a handful of years during college, and I have traveled with men more times than I can count. And they run a very short gamut. The least elaborate setup I've ever seen was a plastic shopping bag with a clean pair of underwear and deodorant in it, for a three-day weekend trip. The most elaborate included two whole pairs of jeans, a clean shirt and clean boxers for each day, deodorant, shampoo, a tooth brush, toothpaste, socks, and hair gel. That was for a five day trip.
Granted, these are mostly teenage and twenty-something guys traveling short-term for pleasure. I'm sure business travel would get a bit more complicated in terms of the suitcase contents. But consider this:
I have also traveled with my fair share of girls. And, being a girl who travels as often as possible for pleasure, I have some experience with how girls pack for a trip as well.
It is nothing short of hellish chaos.
The planning begins days ahead of time. There are lists, and planned outfits, and rethinking of said planned outfits, and attempts to balance space with necessity followed by desperate attempts to just defy physics all together in favor of fitting everything you need into one bag. There is endless running through of the activities planned for the trip, and examining the contents of closets and drawers for what will work best for each occasion.
In the end, there is shampoo, and conditioner. Body wash, and face wash. Shaving cream and a razor, deodorant and body lotion. Face moisturizer. A tooth brush. Toothpaste. Mouth wash. Tampons. At least some makeup and jewelry, just in case we go somewhere nice. A completely different outfit for every single day, with shoes and accessories that match each one. Extra socks, extra underwear. A hair brush, and probably some styling products and hair accessories. A hair dryer, almost certainly. A straightener, just in case. Pajamas that won't cause a scandal.
You're probably reading all that and thinking "this is ridiculous!" Nobody needs all that crap when they're traveling! Who has the space? Who has the time? And you're not alone in your flabbergastedness, friend. Girls get a lot of flak for being high maintenance when it comes to packing for travel. Hell, a lot of us give ourselves flak for it, but consider this: all of those things I listed above are not elaborate extras. Those are the absolute bare minimum required to be considered hygienic and presentable by society's standard.
Do some girls opt not to bother with meeting that standard? Oh sure. But they do so in full knowledge that in order to make that choice, they must accept the consequence of being seen as sloppy, ill-kempt, or even dirty by those around them. For guys? No one cares. No one expects you to wear makeup or shave when you're at school or at work, much less when you're on vacation. But girls? If you plan to get your bikini on you'd better remove all your visible body hair first, or else be the object of others' scorn, disgust, derision, and even pity ("poor girl, didn't her mother ever teach her basic hygiene?"). Because to be clean, boys have to not smell. But a girl's cleanliness is judged on her adherence to standards of beauty.