No missable achievements (plus 40 unknown)
Sign in with Steam or Xbox to track your progress, and:
Loot a corpse.
Break open a supply crate with your hands.
Install your first pistol upgrade.
Receive a tasty treat.
Collect the shotgun.
Feed the snark.
Snatch a Xen grenade from its resting place.
Collect the SMG.
Use the multitool to hack a tripmine.
Kill a grunt by shooting their gas tank.
Pick up and smash 50 glass bottles.
Kill a Combine Heavy while their shield is up.
Use the gravity gloves to loot an item off a living Combine soldier.
Use the gravity gloves to intercept an incoming enemy grenade in mid-flight.
Test your grip on a headcrab heart.
Interact with the playground somehow.