As said before, wear natural fibres cos they don't melt into your skin. I don't wear shorts cos my legs are under the fuel tank in the Auster........ Don't forget, it CAN happen to you.
I also always carry a jacket (denim in summer, leather in winter) cos it might be nice when you take off but walking to the farmhouse in the rain after an unscheduled stop could be miserable with no jacket.... It's also a handy place to keep the wallet, ciggies etc.
I also wear the RAF type green gloves. No it's not a pose, every damn thing in the Austers cockpit is sharp especially the throttle friction and the primer, also the good old Cirrus leaks oil so a wipe around the inside and outside of the cowling is compulsory after aviating and gloves help to keep my pinkies clean and soft
As everything I've owned over the last 5 years has had a transparent roof, I usually wear a baseball cap as well. I started this after realising the the sunroof on the back of my head was getting toasted by sitting under the sunshine coming through the perspex
I'm thinking of getting a 2nd hand RAF flight suit because I've ruined too many pairs of jeans crawling around wiping oil off the undersides of the cowling plus the occasional shirt that comes into contact with the grubby bits. Maybe not appropriate for a modern Piper or Cessna but useful for an oily old bird like the Auster.