"Know your numbers" = exactly which numbers should I know for my business?

I keep seeing this phrase on the great business-fixer tv shows and I want to know more. I know the three basics: P&L, balance sheet, cash flow. I've heard too-quick mentions of others like value of inventory being stored and others. Quickbooks doesn't seem to have reports like that, at least in my subscription level. I might be able to produce them in Excel, if I knew exactly which numbers I should know.

My business is online-only retail sales of high end pet supply products. Toys, beds, collars, that sort of thing, no food or treats. Aside from the basic three financial reports, what are other numbers that I should be tracking on a regular basis?