A few disposable latex (or non latex) gloves can keep your hands clean and dry if you need to fill oil, or other fluids.
If you need to change your tires, a pad for kneeling or a couple of the pads used by flooring installers to strap on to your knees can help.
Some sort of traction pad or a container of kitty litter can help you get unstuck from ice or muddy situations.