How to Make a Lego Claw Arm?
If you're after a simple collapsible solution to reach those items just out of reach, you can start with the following setup:



You can extend this for quite some way, and use longer bricks or beams throughout if you wish.

To finish it off, I'd use a couple of longer bricks with some additional plates on the end to act as fingers, and add some handles (via axles) at the bottom. If you use longer bricks at the ends then the middle pin would need to be offset from the centre to keep it smooth.