Up to you. They're delighted to get anything. I've been very generous with my milkman in past years but we have a new one, so as he's not been around long I will tip him a tenner. I don't have a window cleaner. Usually tip the postman but, again, we seem to have new post people so may not give anything this year. If I see them, might give a fiver.
Ocado delivers to me regularly and I always tip well, rarely have the same driver twice, so will be no different at Christmas.