And it is a very big task. No one is really capable of doing it all. The best solution I have found is to work on things of interest. Read a lot and try things out.
I have not always had great luck in picking out the next big thing but there certainly are a lot of technologies that hold out that promise. And a passing familiarity with a wide range of stuff does keep one busy. Some things of interest to an employer might not turn out to be so mainstream in another 6–12 months. So you have to add in flexibility and an ability to adapt.
And yes, finding a new job that requires you to learn something new, while getting paid, that is kind of the holy grail is it not?