Only if you are trained to do so, if you are not either guide the person to do it themselves or have one of their family members (if available) do it!nice catch. The only thing I would administer is a epi-pen.
#1 is PPE for YOURSELF this means gloves, masks, CPR masks, etc.
I second the ABCs comment as well as blankets to help reduce shock!
Take a class where they teach you how to stabilize the spine!
Broken bones will (usually) not kill you so splints aren't necessary IMO however compromised airway, excessive bleeding and shock will kill you so know how to recognize and treat these things and what equipment you will need to do so!
Keep the kit simple....so many people want one with everything then can't find anything when they need it!