For Michigan and other northern states, keep a sleeping bag in the car incase your stuck in the middle of winter in a snow bank...
A pump action shotgun is nice to have, but it has several drawbacks. First is cost. Second is ammunition. Although readily available, ammunition is expensive. It’s also bulky. The gun has significant recoil. Some family members may find it difficult to use because of the recoil. In the classic EOTWAWKI scenario, Mommy, a couple of children, and perhaps an aging grandfather all need water first, then shelter, food, and protection. A good hunter can bag perhaps 150 turkey sized animals with a case of 250 12 gauge shells.
In the same amount of space, you can store about 6,000 .22LR cartridges. These are effective on game animals from squirrels to whitetail deer. They work on four legged and two legged predators.
I’m not disparaging the need for a good shotgun, and a good centerfire rifle, merely adding a tool that will see more use by more of the people in the group, and will be easier to supply with ammunition.
Also essential in that list are good sidearms. If the S has truly HTF, we can assume that no one is going to care that you are openly carrying a full size handgun when you go about your business. A rifle wood be better, but it gets in the way while digging a ditch or planting crops.
A .45 automatic or a .357 Magnum will be a good choice. Again, they are usuable by most of the potential members of your group. The guns should be stainless steel. Rust will eventually be a problem if they are carried during inclement weather. You can replace ever part of a 1911, except the springs, with stainless steel parts. There are four springs in the pistol and they are cheap and easy to store. In addition to the springs, you should have a trigger, sear, hammer assembly, disconnector, safety, slide stop, plunger tube assembly, grips, grip screws, beavertail safety, bushing, and a barrel assembly.
The .357 Magnum is a better choice if the group is not familiar with firearms. The wheelgun is more forgiving of handling errors than an auto, expecially a single action model.
The Smith and Wesson 696 has 7 springs in it, not including the ones in the rear sight assembly. These can be purchased as apares. Now the probem is the parts themselves. They are case hardened, which offers no protection against rust. You can try to get an old one in good condition. The parts in the old guns were hard chromed to prevent rust. Or you can get a new one and have the parts, as well as your spares, sent out for the plating. One way or the other is essential if the gun is going to last for perhaps ten years of hard use. The rear sight can be bought as an assembly. It will eventually need to be replaced. The rear sight blade is the most likely thing to break, and it can also be purchased as a part. Your stock of spare parts for both guns would fit in a cigar box. Add several bottles of Break Free to your cleaning supplies and you’re all set.
make sure you have at least 200 shotgun shells if you envision being without police protection for more than a few days.