In the human limb skeleton can you identify a bone which is rather feeble and does not have much role in supporting body weight or maintain posture, and doctors use pieces of it to transplant to other broken bones, where necessary?
For bone grafts, they usually use parts of the bones, so their removal should not result in problems with the "body weight maintenance" or "posture."
Parts of the fibula (calf bone) can be used, for example, as a graft to repair avascular necrosis of the femoral neck or congenital pseudoarthrosis of the tibia (shinbone) (International Orthopaedics).
For spinal fusion (joining the vertebra in the spine), they typically use the bone from the iliac crest (the top part of the pelvis) (OrthoInfo).
Other bones that can be used as grafts: