Bread. Milk. Gasoline. Xboxes. What do these all have in common? They're all a staple of most people's consumption — basic products for which there will always be a demand.
Staple also has the broader more abstract sense of being anything that's popular or necessary. A staple of the political scene is partisan bickering; a staple of Broadway theater is the musical revival. And let's not forget another meaning — those handy little metal clasps that hold things together. Though most people wouldn't consider a staple a staple.