“Buy Local” and “Flash Mob” are practically household phrases now, but did you know that people have begun to combine the two, and engage in local, somewhat spontaneous retail therapy en masse called Cash Mobs? It’s true. And this Saturday, March 24th is your chance to be a part of Brooklyn’s very first Cash Mob to celebrate National Cash Mob Day. Local author Amy Cortese, whose book Locavesting is a bible on the subject of investing in our own neighborhoods, is spearheading the group spree. (She also started a twitter feed, @CashMobBKLYN.) On Saturday, she’s inviting all who are interested in supporting a beloved, yet-to-be-announced small business to meet at 4pm at Tea Lounge in Park Slope, with at least $20 in pocket to splurge on something in the nearby shop. After the buying frenzy, the plan is to head to the nearest bar for drinks.