A vehicle save feature anywhere on the map: for example, when you press and hold Y to get out of your car (which switches your car off in IV) it saves it to that location and places a blip on the map; then, you can go anywhere else on the map and when you return your car will still be there (maybe you can use this feature on up to 3 vehicles).
It annoyed me when I had a nice car on mission in IV and I ended up losing it because I had to get out and go on foot or use someone else's crappy car.