If by 'staple food' you mean some sort of processed dry pellet food to be left in the cage for day time snacking - any brand of commercial glider food will be fine - but in general it is NOT a necessary part of feeding your glider.
When most of us say "staple" we are referring to the recipe for a nectar-like mixture that provides the gliders with the protein, calcium and vitamins they need when it is fed along with a wide variety of fruits and vegetables.
None of the pellet type glider foods provide enough protein, vitamins or calcium to be a substantial part of any glider's diet.
Most gliders do not get up to eat during the day. If your glider does get up you can also leave a piece of apple or some dried papaya in the cage for snacking.
None of my gliders get up during the day unless I disturb them cleaning the cage - then I offer a yogie or two and they scamper back to bed.