just because you trust your "safety" doesn't mean everyone else does. don't mess with the trigger until you're ready to squeeze it.
any time you put down your weapon, gear, etc... check it. make sure it's yours. make sure no one fucked with it. there are idiots out there who "accidentally" switch your stuff or screw with your gear/weapons for fun. Don't take such things for granted.
always check your batteries BEFORE a mission. when you're about to engage the BG at 0137 is not the time to realize your optic is about to wink out on you or your illuminator won't work.
always pack more socks then you think you'll need.
treat your weapon like you treat your dog - because, like your dog, if you don't, there will come a day when it will bite you in the ass.
never underestimate the value of a teddy bear.
if you're tight on space, bring the beanie, leave the jacket - the beanie will help keep you just as warm, and you'll probably be in kit anyway.
water and gatorade are not interchangeable.
remember the 3 M's... mess, motors, medical. they make all the difference in the world.
For the FNG medic:
being a medic does not make you a prima donna. don't be afraid to get dirty, learn headspace and timing, recite battle drills, write down freq's, and if all else fails, know where the extra barrels and ammo are.
good medicine is, at times, bad tactics - there's a reason that quote still floats around today.
if you think you have enough kerlix, you are probably wrong.
check your guys' gear - when you get ambushed is not the time to find out they all still have CAT's with the plastic wrapper on, or that they keep jerky in their IFAK instead of Med supplies.