The applicable AR is mostly devoted to uniform wear. The brief civilian paragraph is quoted below:

30-6. Wear of medals on civilian clothes

Retired personnel and former members of the Army (as described above) may wear all categories of medals described in this regulation on appropriate civilian clothing. This includes clothes designed for veteran and patriotic organizations on Veteran's Day, Memorial Day, and Armed Forces Day, as well as at formal occasions of ceremony and social functions of a military nature. Personnel may wear either full-size or miniature medals. Personnel who wear medals on civilian clothes should place the medals on the clothing in approximately the same location and in the same manner as for the Army uniform, so they look similar to medals worn on the Army uniform

I am not sure if "all categories of medals" includes ribbons or not. You see a lot of ribbons worn, but I'm not totally comfortable with it.