Bikes don't usually come with rear racks (although some do). However, most come with mounting points for a rack (threaded holes near the rear drop out and by the top of the seat stays), and then you can just buy any after market rack. If your bike does not have those holes, it may still be possible to mount a rack with p-clamps. If you are handy enough to use an allen wrench, you can install one. Or else you could pay a local bike shop to do it..

This is the rear rack I have. The one distinguishing feature it has is that second set of rails that are lower than the first. This lets the panniers sit lower, for a lower center of gravity, and also keeps the top area free for more cargo. Its definitely not the only reach with the feature, and that feature is not absolutely necessary, but is nice to have.

For panniers, I use a pair Ortlieb Backroller Classic. They are a little expensive, but they come on and off the bike very easily, are water proof (if you roll the top closed; you can fit more in there if you leave it open), and are very durable (I've had mine for years, and aside from some scuff marks, they show no signs of wear). My wife likes the Banjo Brothers Convertable Backpack Pannier, which has the advantage of converting to a back pack, and has more little pouches and stuff.

You can check out the offerings at your local bike shop.

I also have a pair of rok straps and a bungee net wrapped around the top of the rack (they just live there; not expensive enough that I care about any one stealing them), which makes it easy to tie stuff down if necessary.

You could get more advice/opinions on /r/bicycling.

I'm not 100 % sure I could get eight twelve packs with this setup. I think I could get 3 in each pannier with them sticking out the top, and two tied down to the top of the rack. But maybe it would be more like six? Or perhaps I could get more on the top than I think. I don't buy many twelve packs; I guess I will have to go and try this.