.....The knowledge we have is only valuable to us if we have the means and resources.
And some means and resources
will survive. Discounting ONE example is not representative of all of them. I'll wager that we'll still be using modern firearms and not resorting to muskets and bow & arrows. Yes, sourcing gun parts and ammo will be more difficult, but there will be those who have the knowledge to make it happen. Gunsmithing and reloading aren't 21st-century inventions.
We know about modern communications. Crafting a simple telephone is stupid-easy. Two phones, a resistor and a 9 volt battery and you've got an intercom. I agree it ain't the internet but such a simple system has a huge number of uses.
I could go on, but I'm sure you're already typing a scathing retort, so carry on.