Yup, I keep a separate kit just for my truck. Is addition to all the regular stuff, I also keep ratcheting tie-downs. bungies, and rope. May want to consider keeping a tarp as well to keep things covered.

Yup, one of those things that can be tough to manage. I've tried the "don't use it unless it's an emergency" route - but that causes you to not test your stuff and in some cases, things deteriorate or expired before they're used up (waste of money). And I've tried the "use it cuz you got it" method - which keeps you in practice with the stuff you have, but you constantly have to remember to replace stuff.

Of the two, I think using your stuff is better, if you can get in the habit of remembering what you need to replace and replacing it quickly.

I think the best solution is to have about 100 identical packs and use them like disposable razors. When you use anything of the the pack, you just throw it away and get out a fresh pack. (I'm kidding, of course).