Caribou Coffee Coupon: Buy One Get One FREE on Mother's DayMay 10, 2012 by Mitchell Wischmann This post may contain a link to an affiliate. See my disclosure policy for more information. EXPIREDThis deal has ended.This Mother’s Day, May 13th, Caribou Coffee is offering buy one get one FREE drinks! You can either print out the coupon, or show it to the cashier on your phone. Limit one offer per person.What’s your favorite drink at Caribou?