12. First-Aid Kit
A first-aid kit such as the one from Adventure Medical Kits can help you in a wide variety of survival situations, ranging from a far-reaching disaster to an accident while hiking.
Most first aid kits can be packed in their entirety within your checked luggage, but you may need to modify one slightly in order to bring it as part of your carry-on.
For example, if there are any scissors or sharp items, you are not technically allowed to bring them through the screening checkpoint.
When you consider the possibility that you might need your first-aid kit during the aftermath of an airplane crash, it makes sense to forgo the sharp items in order to keep your kit with you at all times.