To earn the Pack Rat ribbon, a farmer must own decorations. Any decorations may be used and can be bought from the market. Hay Bales are often used to earn the ribbon, as they are a lot cheaper than most other decorations.
It is not necessary to actually display the decorations on your farm. Decorations in your gift box also count toward earning these ribbons.
Fences serve double duty toward this ribbon and the Fenced In ribbon and so do Hay Bales toward the Baled Out ribbon.