I don't need to explain this, do I?
With the popularity of Sidney's My Sari-Sari Store, and the almost (always) featuring it in Mike's The Fiery Scotsman, I have no doubt that most bloggers already know what sari-sari store essentially and culturally means to us, Filipinos.
Sari-sari literally means "various kinds". So, in essence, it is a store that sells various kinds of goods, mostly food items and other basic necessities (sugar, salt, candles, matches, detergent, etc.) and others (cigarettes, alchohol, etc.).
Economic importance: instead of buying the whole pack, you can buy in units (tingi system) therefore it's much cheaper!
Social and cultural importance: a place to socialize and meet people, better than staying inside the house, cheaper than hanging out inside Starbucks (the store sells instant coffee too!).