h/t Gun Free Zone and 90MilesFromTyranny
You should print this out and laminate it.
One in each of your first aid kits.
One in wallet size for every member of your family, group, etc.
And if you have a dedicated medical treatment area, a larger size wouldn't go amiss.
As this makes clear from the left-most column, O- in the Universal Donor.
As the bottom line makes apparent, AB+ is the Universal Recipient.
You would be wise to know your own compatibilities in both respects, but such a card removes the memory work for those disinclined.
You, your family, and whatever tribe you're around do know your own blood types, right?
If you don't there are a number of ways to find out.
Including giving a pint to the Red Cross at a blood drive.
Hopefully it's just over-preparing for something you'll never need.
But don't be the Darwin Award punchline in some future version of For Want Of A Nail...