Organ Stop Pizza in central Mesa kicks off its 50th anniversary celebration – ‘‘50 Days to Celebrate 50 Years of Fun!’’ – on Saturday. The promotion, which runs through Oct. 8, will feature nightly merchandise and food giveaways, a $50 meal deal (two large pizzas with unlimited toppings, two appetizers, and two pitchers of soft drinks), and half-price sundaes on Sundays. Organ Stop’s 700-seat dining room is home to the 95-year-old ‘‘Mighty Wurlitzer,’’ the largest and most valuable theatre organ in the world, which is the star of nightly shows ranging from classical to pop music.
