If you're not a main character, try to make sure you're the minor character who mysteriously disappears, is presumed dead for most of the movie, but who turns up unexpectedly at the end. Note that even if your plan takes into account all possible situations, it will not cover the one that actually occurs. During a lull in the action, never mention that you have any goals in life, anything to look forward to, or any loved ones that you can't wait to see again. Doing so decreases survivability to zero. Of course, the item WILL be waiting for you in the car as you go to leave.
Monsters only attack overly horny teenagers.
The reasons should be self-explanatory.