Prepaid expenses include anything that was paid in a year but it will be utilized or consumed in later periods. For example, paying your insurance policy in advance is a prepaid expense.
I imagine that by saying supplies you mean stock (inventory). If yes, then no supplies can not be a prepaid expense. The closing stock is already adjusted to reflect the fact that you have received stock that is not sold yet. Similarly, sundry equipment (for example office supplies) are part of your fixed assets (part of the property, plant and equipment) so they are not prepaid expenses.