Hmmmm….I say carry your helmet proudly into meetings. At least that provides an obvious, but subtle, explanation for a slightly disheveled appearance. Makes you look badass too.
For women, sometimes a headband works to tame unruly hair. Pushes it back neatly and allows it to dry. A camping microfiber towel is lightweight and absorbs a lot of water. I suffer from frizzy hair so I now keep a flat iron at my desk.
If your pannier or backpack isn’t waterproof, try Hefty’s Jumbo Slider Bags (essentially huge ziplock bags). I use a packing cube for my clothes; helps keep them from getting wrinkled.
I agree that security at the different fed buildings is a problem; even if you don’t show up on a bike. I suppose you could just inform your escort that you will need 15 minutes before the meeting because you need to change out of bike clothes and ask that they escort you earlier than expected? I expect any “important” person would simply send someone lower ranking to fetch you and show you the nearest bathroom. But maybe not…
What I absolutely hate is having to change in a non-handicapped stall. Now that requires some gymnastics at times. Always good to ask for a bathroom with such a stall.
I wonder how the Dutch do it?