C) O
For a patient with blood group O, which is often referred to as the universal donor for red blood cells (RBCs), packed RBCs from a blood group O donor can generally be used in the cross-match without any major compatibility issues. Blood group O individuals have neither A nor B antigens on their RBCs, making their RBCs compatible with most other blood types. However, it's essential to follow specific protocols and procedures in a medical setting to ensure safe blood transfusions.