Did someone ask a question, post a poll, and expect an opinion...?
Alrighty, then!
If you can afford to get it all NOW, here's what I think about it...
The choices are pretty good, but I'd change a couple of them for couple of reasons.
First, I like to have the 'safety' in the same position if at all possible. This would make the 870 backwards from your other choices.
Second, the SKS is a good choice and a very serviceable rifle, but you've indicated you want an M1A in .308.
So, based on that, I've picked a couple of different guns to put into your list that would enhance the way your choices work in concert with each other.
Here's what they are and why I gave my opinion on them.
I hope you get it ALL!!!
1.
Ruger 10/22 .22LR
Good to have a .22 rifle.
Many options to alter it to suit your taste or fit into the 'look' you want with other guns in your collection.
Safety at the front of the triggerguard.
2.
Ruger Mini-14 Ranch Rifle .223/5.56x45 NATO
Ammo is reasonbly cheap and effective and common.
It's like a LITTLE M1A, literally designed that way.
Accurate 'enough' and reliable magazines are available.
Scopable, if needed.
Safety at the front of the triggerguard.
3.
M1A .308
Ammo is reasonbly cheap and effective and common.
It's like a BIG MINI-14.
Safety at the front of the triggerguard.
4.
Winchester 1300 12-gauge pump SHOTGUN
Relatively inexpensive.
Has a 'speed-pump' feature.
Safety at the front of the triggerguard.
If I were to choose only 2 of the above to start with, it'd be difficult.
Probably the .22 & .308 would be most useful for survival purposes.
For Civil Unrest, the .223 & 12-ga. would be my choices.
That's why I said get it ALL if you have the means, and keep it all familiar to make it easier to transition from one to the other.
Good Luck. Have fun shopping!