It is common to use a full set of clothing, including underwear, socks or stockings, and sometime even shoes if so desired.  The clothing can be from the wardrobe of  the deceased.  Traditionally, men have worn suits and women have worn dresses or pant suits.  You may want to consider a special outfit that your loved one wore, such as a dress or suit worn to a grandchild's wedding; or, it could be an outfit that your loved one wore most--like jeans and a T-shirt.  You may wish to buy a new outfit.  There are also burial garments available at the funeral home in those instances, for example, when someone was in a nursing home for a long period of time.  Whatever makes the family the most comfortable seeing someone in for their last goodbye is what is important.