If you are in most any 'populated' area, good look bugging out.
while movies often get a lot wrong (and sometimes intentionally) one of the things they usually get right is how jammed and useless roads out of major cities will be once the evacuation begins.
Doesn't matte what the looming disaster is, once the panic starts, only the very first few to leave will actually be able to get away, other than on foot.
Unless, of course, you're wealthy (or works for someone who is) and you can fly. This can get you away, but then, you have to land, somewhere...
One of the things most commonly ignored about "survival" guns, ammo, and reloading is that the only thing you can count on is what you already HAVE and have with you when things turn bad.
And that includes tools as well. All of the "you can make this out of that" is good to know, but you can't make "this" if you don't even have "that" to begin with.
I also don't think its realistic to indulge in the fantasy that you'll be able to find "useful" things in the "rubble". First off, you're competing with everyone else who "survived" for resources and the odds are good you aren't going to be the first one there looking...
The difference between looters and scroungers is looters get shot or shot at.
Point here is, if you don't already have it, you aren't likely to be able to get it, even if civilization doesn't completely collapse. We've had a taste (and a sour one) in just the last few years with shortages of goods with just a partial collapse of our system.
For me, "survival" reloading is something you do at your retreat, where you ALREADY have stockpiled supplies and tools. Nothing electric is going to be useful for long, once the power goes off things that run off line power are about useless and things that run off batteries are little better unless you have a lifetime supply of the right batteries. So, forget about digital anything, have balance beam scales, and things written down on paper (like you load data) cause there isn't going to be an internet to look things up on, etc.
the ultimate "survival" gun when you are out of premade components is a flintlock but you do need a few accessories (a mold is vital, and a few spare springs are a very good idea). The rest of what you need, you can make, though the effort involved is not a trivial task.
As for the situation where you find a box of .40 but you have a 9mm, I wouldn't bother with the work to try and salvage or adapt what you could to fit your 9, I'd keep the 40 ammo stashed in hopes of finding someone to trade with in the future.
Short form of an old story about bad times...
Guy puts his money in gold/gems, knowing cash will be useless...
times are bad but not the absolute worst, trade still happens a little bit...
He's hungry, famer has chickens, he wants to trade, farmer says what you got to trade? I got gold!!is the reply.
Farmer can't eat or use gold/gems, but agrees to part with A chicken for a handful of gold coins. Guy is outraged, this is gold! Farmer says "just consider it an epensive chicken!"
different guy, same farmer, wants to trade, farmer asks, what you got to trade?
Guy says I got half a box of shells that fit your .30-30 (or .22LR). Farmer says, "how many chickens do you want for them??"
point here is that value is situational, and when things go really bad, the only things you are going to be able to count on getting is stuff you already have.
So, get (and keep) what you think you'll need, NOW, if you haven't already. Its not likely to get easier soon, and it may never get any cheaper....