Rear wiper would be cool. I always wanted to install the JDM rear wiper on my car. Even with a pretty steeply raked rear window a lot of crap gets on there.
And I always engine brake my car. It's just more fun
Normally I downshift until I'm at about 10mph in 2nd and then shift into neutral (obviously I use the brakes too as needed). If I'm in heavy traffic I just use 1st gear and don't use the break at all unless I come to a complete stop. Usually you can get by without having to stop by leaving a ton of space to the car in front of you. Just watch the truckers, they all do it. Still on original clutch at 120,000 miles (and only had to change the break pads twice, 2nd time was just a few months ago)