Things to draw when you have nothing else to draw?

Anything and everything. Start small and simple. Draw basic shapes. Square, circle, triangle. Work with shading to make the shapes look three dimensional. Now work on three dimensional shapes, a circle becomes a sphere; a square becomes a cube; a triangle becomes a cone or maybe a pyramid, once more shade your shapes, this time add a cast shadow.

Then try something a bit more difficult.

An Apple starts with a circle and you modify it for a more realistic shape, then shade it to make it look more real, add a shadow, maybe a bunch of small circles to look like grapes, next thing you know you have a "still life" (basically a bowl of fruit).

A house starts with a cube with an elongated triangle on the top...

A cone can become a hay stack...

As you start to get more practice you will learn to see the basic shapes in the things around you. This will make it easier to draw them realistically.

Eventually you will be able to draw not only things you see around you, but also things from your imagination.