I loved this scene. The whole way through I was trying to guess what items Locke would pick in comparison to what he "should" be picking.
Was Alpert trying to recruite Locke? The knife, as you've said seems to be his logical choice and yet that was the item which clinched Alpert's displeasure, perhaps even disgust? Since he seemed to have been tracking Locke's life I'm curious as to just what items he wanted Locke to take - and why he wanted him to take them.
Also, the main thing I'm curious about is whther or not Locke would have chose these items if he'd be under less pressure. Did he take those items because he was
drawn to them, or did he take them because he thought that Alpert
wanted him to choose them?
Another point I'd like to make is that despite this "failure" of the item test, Alpert continues to try to recruit Locke - the science camp as a teenager. I wonder if Alpert thinks Locke's view's have changed by this point, or if he just wants Locke to fufill his destiny. If it's a time loop, did he need Locke for something?