I use to crack my neck all the time, but what I did to stop (it might seem sort of weird) is when it felt like it had to crack I put my head up as far back (not so far back you can't breathe) and I kept like that for 3-5 seconds (not minutes). Now for me it doesn't feel like it has to be cracked anymore so I hope it works for you too. As for the fingers, I don't know how to stop that. The other answers will help too.
A good way to stop cracking your fingers, neck and back is through slowly adjusting from doing it. You can keep yourself busy by doing other activities, so that your mind is preoccupied. This will reduce the times you are free and which is when you are likely to crack your fingers and neck.