The tone of this implies that lining up a new job without first quitting is outdated and negative. From the other side, quitting before having a new position can look irresponsible.
I have never quit a job without another lined up and have done quite nicely, myself. Why ever invest in trashy projects when one can get good jobs quickly and easily?
I suppose sleep and videogames aren't great answers. Taking time off to travel or explore some other interest is almost certainly fine in SV.
Ultimately, I think most places are so hard up to find qualified candidates that as long as you pass the interview and don't come off as a total slacker, you're probably fine. But if you're career-minded and applying to a place that has their career tracks worked out (read, not most startups), you probably want to give that impression to your future engineering manager.