What to do between submission replies?

I am in waiting territory at the moment. I have a number of agent and publisher queries pending. Replies to some of them are due soonish - but not soon enough. The usual advice is that you should send away a query, then get on with writing or editing the next WIP. It's good advice. Very good - in theory. In practice, you can't help being on edge until that answer comes back. Maybe this time - in the words of the old song. It's what all writers hope for. It does happen to some people. The trick is to keep up the belief that it will happen to you, one day.