Ben Affleck and Jennifer Garner have risen up to do some coparenting again this holiday weekend ... walking around with their son Samuel on Good Friday in Los Angeles. The former couple walked on either side of their 14-year-old son ... looking casual yet fashionable -- with Ben in a button-down and khakis while Garner rocked jeans and a long cardigan paired with a gray T-shirt. Check out the photo ... Ben's cracking a big smile -- seemingly at something his son just said while Jenn eagerly