There is one gift that you can give that doesn't cost a thing and could mean the world to people you don't even know. Of course, we are talking about the gift of life through a blood donation.   The American Red Cross says the national blood supply has dipped to concerning levels and could force hospitals to hold off on essential blood and platelet transfusion for patients, if more blood cannot be collected.   There are some blood donor clinics being held this week and next in our area.