Use bricks or bottles to lure an infected into attacking a human

Win the water gun fight

Engage in all optional conversations

Win the brick throwing contest

Find all training manuals

Break into every locked door using shivs

Ride the sewer contraption with Henry and Sam

While in stealth, turn off the spotlight generator in Pittsburgh

Complete the game on Normal.

Escape from the ship.

Use psychostimulants.

Complete the "Happy Birthday" videotape within 5 minutes.