Is there anything more refreshing than a cold treat on a hot summer day? Sonic Drive-In is making the summer solstice a little cooler with 50% off all shakes on June 18. Choose from 25 sweet, delicious flavors. Each shake is topped with whipped cream and a cherry, of course. Sonic has changed its shake menu and divided it into two types — Classic Shakes and Master Shakes. The latter are slightly higher in price. There’s no limit, so everyone can get a “shake down” without breaking the bank.