I had an opportunity to pick up a nice Jansport external frame backpack at a very reasonable price at a garage sale. I really like it, however there are several parts of the pack that I don't understand exactly what they are for.

I've attached a photograph of it with the parts in question highlighted in yellow.

1) There is a semicircle set of zippered teeth with a zipper pull that has nothing to attach to it. I assume I'm missing something that would have the corresponding teeth so it could be zippered/attached to the back - possibly a hydration pack? Any ideas what this might be?
ear the bottom with several

2) There are 2 clips on each side on the back that appear to connect together, however the lengths are WAYYY short. It appears as though this is where a strap would connect across the back of the full pack to cinch it tight, - so am I missing the extra straps?

3) Lastly, there is the hard rubber portion near the bottom with slits - my assumption is that these are slits where I could attach more items using straps again, but I'm not positive.

Can anyone give me some expert advice? I love the pack, but I want to make sure I'm using every option available to me.