The original I have is made out of paper essentially the same as normal computer paper. It has yellowed quite a bit, but I am assuming that is age. Nonetheless it is best to avoid the super-glossy or super-bright computer paper. Cheap stuff works best.
I used scissors to cut on the exterior outline. At the top there is a small section that dips below a horizontal line. Follow the dip (the horizontal line is a score line) Then take a single hole punch and punch out the three holes in the right panel.
Score all the interior lines. Fold the right panel (with the hole punches) back so that it’s underneath. The inside of the left panel gets a stripe of glue and is folded back (so that it’s over the right panel). The bottom panel (patent pending) gets glue on the inside and is folded back. Here is the tricky part. Looking at the main body of text there are two flaps (a small one and a red one). The small flap will be glued down securely. The red flap gets only a spot or two of glue (so that it can be pulled up easily). The trick is that the two cannot really separate without tearing the paper, so they need to be glued simultaneously
These were copied from one found in a First Aid Packet, Carlisle Model. They contained 5 grams of a white crystalline powder (sulfalinamide). The purpose of the powder is to prevent infection, but because of how it was administered (externally) it may have had limited usefulness and may have even been harmful (introduction of foreign particles). Still, it was training and practice to apply the powder.
This is an easy reproduction since it doesn’t require any fancy paper. It’s also one of my favorites since it can be used during a reenactment. Normal table salt looks pretty close, but be sure to put it into the packet before you glue the flaps town. These could be used in conjunction with a wound card system by printing the wound card information (alive/dead/whatever) on the inside of the packet. The wound card information would then be unreadable until the sulfa was administered.