Zombies Ate My Neighbors and Ghoul Patrol (UP)

All five of the weapon types in Ghoul Patrol can be found in the first level and picked up within a minute.

As you start, you'll already have the Crossbow and just to your left is the Martian Gun to pick up. Go down past the flying books, then to the left and up through the gap in the shelves; press to jump up on the desk ahead and grab the Key by the door (don't go through it), then head to the left side of the room from here to pick up the Machine Gun on a far desk.

Now head back through the gap in the shelves and down slightly to the right will be a door. Go through this and to the left inside to grab the Cannon lying on the floor, then head back to the right, get another Key by the wall and go down through the door. You're now outside; head straight down, stepping around a log on the way, until you hit a wall, then go to the right along it and near the corner is the last weapon, the Laser Gun. The achievement should pop after picking it up.