How to Survive Being Buried Alive ~ Don't Be Like Ryan
You've managed to piss off the wrong person and find yourself six feet under in a pine box, alive. What do you do?
As someone who's watched a million episodes of 1000 Ways to Die, I've researched and mentally prepared for these types of situations such as multiple ways to escape from the trunk of a car, zip ties, etc. Not that anyone has ever cared to listen to this valuable information.
You can imagine my dismay while watching Buried with Ryan Reynolds. Spoiler alert, he spends half the movie buried in the coffin chatting on the phone, on hold with some useless twats.

Screaming at the TV, "You're not doing yourself any favors Ryan! Where have your looks gotten you now?"
At least there is some practical information for how to break out of a cheap coffin.
Make an air pocket with your hand, or take it all off

Tie your shirt around your face if you can. This will prevent any debris from getting in your nasal passages on the hike back up to the land of the living.
Try to break the center of the lid
Make use of any hard objects you may be wearing. Making a small crack will relieve pressure and make the next steps much easier.
Escape
Move dirt to the outside of the coffin as it begins to seep through. Considering that the average burial depth is 6 feet (I'm 5'10"), it should be relatively easy to pull dirt away from you and stand up to the surface.
I hope it doesn't happen to me!
Chances are, no, I just like researching these things haha