Hey! Glad you found some good mud! First, definitely bring a couple changes of clothes. Typically, where there's mud, there's water, so even if there is just a tiny bit of water (and even if it's muddy water), I find that cupping water with my hands, and rubbing the water all over my body cleans off most of the mud. Depending on the mud, it can also dry and flake off pretty easily (clay, for instance, flakes off when dry). Another idea is to pack a towel or t-shirt you don't care about, and once you're wet, wipe off some of the mud, then air dry a bit. Once you're dry, you'll still be dirty, but you can put on clothes over the dirt, get home, and shower the rest off. Good luck, and message me if you have questions. I'm a mud expert!
Here's how I do it: 1) Get old towels. Dark colors are better. Cover your car seat with a couple before you get messy. If you have leather seats, that will clean up easier.
Take with you an old backpack with sweatpants (dark) and some kind of t-shirt or sweatshirt.
2) GO WILD! Get muddy, flop around, fill your panties (ok, maybe that one is just for me, haha), etc.
3) Try to clean up as best you can on site. You may not be able to find much water. I never could.
The sweatpants and top cover will let you get back to your car. The mud will seep through and you'll be dirty but it won't be terribly obvious if they don't look closely.
Preparations the trick. I use a couple of towels, a blunt kitchen knife to scrape off the worst, a cup to pour water, a wad of paper kitchen towels, a long handled kitchen scrubber for the back, maybe a bottle of water for a final rinse to the face, and a mirror to check. Maybe even cotton buds for the ears.
I take warm water with me. amazing what a couple of litre bottles will do, a little bit at a time... and shampoo! Gets you clean enough to get home and have a proper shower.