A PFAK by its very nature is small. Your only option is really only to be able to treat minor injuries. When you start traveling then you need to carry larger or supplimental kits to deal with greater levels of injury. These other kits should be geared to meet the most expected types of injuries. As you said even these have limits. Shy of a fully equiped and staffed ER you can't cover all situations. It just doesn't fit. So you gear up for the most likely events and then try to improvise the rest.