Hey - An SBR is great for all kinds of stuff from impressing the chics at the range with your cool operator stylings, to being easily concealed, lighter to carry and handy indoors in the event this were a real SHTF.
But it is way down on my list of needs. More water, food, meds. fuel, comms, tools, etc...
And having two guns and backup that you are super skilled/confident with is way better than an arsenal of which you have passing familiarity.
I am still very much of the mind that the grand firefight for which all prepare and hope for (yet will pee our pants if ity happens) is mostly a myth for most SHTF's we will encounter.
The reality is that over 30 days we won't shoot 10 rounds. But as always, better to have them when you need them than not have them!
If I really need to go from zero to ready I'd go out and buy a use 870 of any barrel length, and get three boxes of buck shot and one of slugs. Then I'd get a used Glock 19 and a box of Federal SD ammo, and a couple of boxes of 115 FMJ and call it ready. After that 30 days of food and water is more important.