Dynamic Bones

Simply put, dynamic bones work pretty much the same as regular bones, but they are made dynamic in Unity. You will add bones to the rig up the subject the same as normal, applying weights where you would normally.

Something to keep in mind when rigging up hair or other equipment with dynamic bones would be to ensure that the shape keys don't ruin the effect of the weighting.

Additionally, especially long hair might need an alternate hair model with shorter hair to fit within the confines of a closed helmet, and things like ponytails can be made into separate objects so they can easily be hidden when a helmet is put on.

Remember to parent the dynamic bones to the correct location. In the case of dynamic hair, parent the additional bones to the head bone.