1: Catalogs
Catalogs are going to be the hardest hit because of reliance on a healthy economy to sell parts. Ordering something custom out of a catalog for your car could take months. That might not be acceptable for those trying to get ready for summer. Catalog car parts are some of the rarest.
If you rely on Hot Rod catalogs to show you the latest gear for your muscle car, there might be a heavy wait on those parts.