Pick the clothes, "S" can the buttons and replace with Velcro. I did this on the inspection BDU's in the army. Just not the one's for the field due to noise discipline.

5-11 just came out with a new pair of tactical pro pants. They are not BDU standard but are very close to it and much lighter. I tried on a pair and was impressed.
5-11 tactical pants

I personally wear Mountain Hardware Canyon pants and have put them through years of off trail abuse with zero defect. No cargo pockets but the depth of the 2 front/2 back more than make up for it. Plus I use vests or packs for heavy carry instead of stuffing pants.

The lightest stuff is going to be from North Face, Mountain Hardware, Columbia, heck even Under Armour has some good light and strong pants. The rub for me is most of these that have cargo pockets are also zip offs and I don't do that style.

For those activities I prefer an old style Mil SEEK 2 pocket
vest, it will fit well under a float vest.

The link goes to the poly/cotton version. I have nylon 5-11 trousers and they are very comfortable in the rain. Add some Smartwool/other wool long underwear and they should be good in cold and wet.

Thanks for the suggestions, Comms. I have some of the very lightweight nylon pants and shirts for backpacking and casual outdoor use from various makers. By the way, Academy Sports has some really nice models, near copies to Columbia, etc., at very good prices, zip-off or not. I now have enough use on them myself to say they hold up well.

What I need are some in the recent BDU pattern, in khaki, which are issue for the federal agency I work for. Unfortunately, the issue is in poly-cotton, which is still way too hot, heavy and slow drying for me, especially since I know superior fabrics are now available. I even looked into having a half dozen or sets made up for me, without success.

Well,

When you say Northwest Florida, how close are you to Hulbert field? The fellows in the USAF that wear the Aussie brimmed hats might know of a good seamstress in that area. Long before the new (8 years or so) uniforms came out, the SOCOM boys were modifying BDU's to fit their needs.

My favorite mod was the SDU5 beacon pocket on the sleeve.

I work and train with some of those guys. I'll ask around again. It was a few years ago that I last looked into it, mostly online. I had a few leads on tailors, but I think I was looking for a sewing pattern. I should have asked last weekend, when we were all sweating our posteriors off in heavy, sweat soaked poly-cotton tees. My job is safety officer, which means mostly being the water-boy and official rest and rehydration nag. We even had a major discussion about heat stress issues. But I'd long since dropped the unform replacement project. Funny how you get so used to "what is" that you forget about "what could be."

I took an old set of "Cook's Whites" (old faded woodland BDU's) and a seam ripper and made my own pattern. Took some time, but it worked when we needed some OPFOR uniform and grew tired of the old "chocolate chip" desert BDU's.

I don't know what the new Army ACU is like, but it looks darn functional.

If using the old BDU pattern, sew the velcro to the "Button Flap" under the pocket flap so the stitching doesn't show.

But then on my inspection uniforms, I also had the pockets cut and the bellows reversed into the uniform instead of bellowing out.

I should say that these uniforms were only for guard mount inspections and street MP duty. In the field, I had regular issue BDU's.

I think most seemed to have missed the point. Scafool seems to have come closest.

The point is to keep survival kits, and all gear attached to you, compact and streamlined.

While keeping a knife easily at hand sounds like a sound solution in this case a knife may have been exactly the wrong solution. Slashing desperately and blindly at a grab line while being buffeted by whitewater sounds like a fine way to hole the raft. Tangled in the grab rope of a raft is bad. Tangled in the rope of a raft that is no longer stable and under control because a major flotation chamber is holed is far worse.

Now I don't object to having a knife of some sort handy, options are good, but the knife has to be used with great care and only where it makes sense. Also the sheath and knife have to be mounted and positioned in such a way that it does not create a risk of being tangled. Some thought might be given to the sort and size of blade you carry. Knives designed for use around life rafts often have blunt points and it would seem to be common sense that the blade should be relatively short. Most knives purpose built for survival use around rafts seem to have blades only about 3" long. A shorter knife would also seem to be less likely to get snagged or cause unintended damage.

Survival gear in general should stay out of the way until needed and impose the minimum burden possible on the person carrying it. Small and light with a few well selected and highly adaptable pieces is better than a larger kit with more specialized gear. Particularly if the kit gets in your way. The most important, and comprehensive piece of kit is what you carry in you head.

Okay, no one else said it so I will. The force of water is such that 5CFM can bend steel.(I learned that on the History channel the other day)
It is not outside of the realm of probability and well within the range of human experiences for water to literally rip things off that are attached to you.
If I were to carry a survival kit on my person when whitewater rafting, and I do, I carry it beneath the flotation device. There is little likelihood of it getting snagged, washed away or damaged. The vest offers some protection and since you would not need any of those items until after you hit dry land, their access or lack thereof is inconsequential.
The survival kit on a fighter plane is not accessible until after the jet jockey punches out for much the same reason.
I would have a knife on the outside of your PFD as well as a backup in your survival kit...