Break out of the Combine prisoner transport vehicle.
Enter the Quarantine Zone.
Pick up and smash 50 glass bottles.
Feed the snark.
Interact with the playground somehow.
Represent yourself with a specific prop on Russell's map.
Measure Russell with the Geiger counter.
Catch Russell's ammo magazine before it hits the ground.
Receive a tasty treat.
Test your grip on a headcrab heart.
Collect the shotgun.
Enter the explosive Xen infestation.
Stop the prisoner transport train.
Reach the Northern Star.
Get creative turning the power back on.
Escape the underground pit.
Collect the SMG.
Shut down the substation.
Defuse a roomful of explosive barrels.
Escape the distillery without killing Jeff.
Kill the annoying headcrab before it breaks everything.
Catch a bottle falling out of a cupboard before it breaks and alerts Jeff.
Reach the aquatic exhibits.
Solve the tanker yard's electrical puzzle and escape.
Start climbing the water tower.
Wake the Strider.
Get to the superweapon.
Make your choice.
Loot a corpse.
Break open a supply crate with your hands.
Install your first pistol upgrade.
Kill a grunt by shooting their gas tank.
Kill a Combine Heavy while their shield is up.
Use the gravity gloves to loot an item off a living Combine soldier.
Snatch a Xen grenade from its resting place.
Use the multitool to hack a tripmine.
Use the gravity gloves to intercept an incoming enemy grenade in mid-flight.
Stay close to Jeff for 10 seconds (but not too close).
Bring Russell a bottle of vodka.
Bring a garden gnome with you to the Vault.