With the proposed changes to blood regeneration and blood bags, THERE ABSOLUTELY MUST BE some way to mark the bags with a blood type. Either manually with a pen, or have it done on it's own when the bag is filled.
As of now each person must carry their own blood bag in order to not die on accident. It makes a person who acts as a medic have to either have a super good memory, or keep blood bags of different types separated. Which is mega impractical.
Please do not overlook this.
This is set to become a common problem very soon if we're being encouraged to test out blood bags and regeneration. Having the bag automatically identify itself would be the most convenient (Built-in blood test?) and easiest to implement.
I think the most realistic and practical way is to be able to attach paper on to things and then player just write down whatever on the paper.
I like the idea of writing your own note and tape it on the bag.
That way you can still make your own code for the blood types to make it harder for looters to identify the blood type in the bag they just looted from your dead body.