Knife:
I have a Gerber micro LST in my PSKs. Blade isn't a lot bigger than an xacto blade, but I'm fumbled fingered enough (even without a survival situation) that I'd like something to hold on to. I think there are several sizes of the LST--micro, mini, regular, jumbo, etc... Packs really flat and light.

Tarp Clips:
Not sure you want to include such a special purpose item in a PSK, but another commercial version is
http://www.leevalley.com/garden/page.asp?page=45515&category=2,43288,42182&abspage=1&ccurrency=2&SID= which I've used pretty successfully with 4mil plastic sheeting. Lee valley also carries their big brothers http://www.leevalley.com/garden/page.asp...=2&SID=