Some of the best fishing tips have nothing to do with fish. This one is about what happens after the last cast, and it is one of my favorites for long days on the boat, multi-day trips, and any outing that ends with a long drive.

The tip: pack a good chamois
Keep a quality chamois towel in your boat bag at all times. I use a mini chamois from Nomadics, and the reason I like a chamois over a regular towel is that it soaks up a lot of water and stays compact. After you pull the boat out, find a private spot, step into the river, and rinse off. It takes a few minutes and does two things: it gets the day's sweat, sunscreen, and fish slime off you, and it refreshes you after hours in the sun.
Why it works
Think about the alternative. You spend all day sweating under waders, layered with sunscreen, and then climb into the car for a multi-hour drive in the same clothes. A quick rinse and dry-off changes that completely. Friends I have shared this with have said the same thing: they had never thought of it, and they had been sitting in sweaty clothes for years.
Make it a system
Pair the chamois with a spare set of comfortable clothes left in the car. I like loose cotton pants or something soft for driving. Rinse, dry off with the chamois, change, and you are ready for the road. Use common sense on the privacy and water temperature front: choose a quiet access point, and in cold weather, rinse quickly and dress fast. Wring the chamois out afterward and let it air dry so it does not sour in your boat bag.
Chamois towels are inexpensive, and the same one doubles for drying your hands, your rod handle, and the boat seats during the day.
Gear
Check out the FFIP Logo Anglers Coffee Mug for the early start before the trip, and for the towel itself, stop by your local fly shop and ask what they stock.