One of the things I always liked about LucasArts adventure games was that you could never get stuck in a dead end (I remember not being able to finish Hitchhiker's Guide to the Galaxy because at the very end, Marvin asked me for the only tool out of 17 that I had failed to pick up before the door locked behind me).

Presumably diagrams like the ones above helped you avoid this sort of thing. But did you use any formal techniques, or tricks to make sure the player couldn't get stuck?

One that I've noticed is to use an object that will be crucial in Chapter 3 to hide the key for getting out of Chapter 1. Any others?