And a disaster kit, tailored to the most common disasters in your region. If you have a first aid kit you already have a large portion of what it needs!
Very important that whatever first aid kit you get has a tourniquet, or that you buy one separately.
They are easily the most important life saving device in any first aid kit. 99% of the time you won't need it for normal cuts but when you are dealing an injury that needs one you WILL regret not having one.