You hopefully won't
need to use this, but accidents like getting shot happen in the field. You can press "use"
and click on the First Aid Kit in the inventory, or select it like you would select a weapon,
then click on the man that needs health.
TIP: You don't get much health from a First Aid Kit, so if your badly hurt,
you may want to consider reloading your save game, instead of using lots of precious First