We have it about half the time in our house. Currently, not. Calling it a “necessity of living” is a bit odd to me.
We have all 3 plus baking soda & powder.
Yes, all. But I have not checked the flour in a while, it may no longer be fresh.
Beans, barley, rice, etc.
We have some sea slat in little jars our daughter gave us, which we use on baked potatoes, only rarely in recipes.
As for sugar we have regular sugar, brown sugar and confectioners sugar. That is mostly used for beignets.
We we haven’t had in way too long.
We always have all three in the pantry, primarily because my wife bakes regularly, and thus, uses all of those ingredients regularly.
Same here, and for the same reason as my first answer. 
Flour can be used for dredging chicken, fish, veggies for baking, or making a roux or gravy. I have regular flour, pizza flour, whole wheat, and corn meal.
Salt is a standard table condiment. It’s used to prep meats for cooking. I use it to clean cast iron pans. Also pickling. I generally have kosher and table salt.
Sugar for coffee, tea, etc. It goes in some marinades, and any number of recipes that aren’t baking. I have white and dark sugar, honey, and molasses.
Hmm. So many people who don’t have soda. None of you have kids in the household? Or…Ah, maybe I’m biased. Well, almost certainly. The thing is, I don’t drink either coffee or tea, and also suffer from insomnia. Some days I HAVE to get caffeine from somewhere or risk falling asleep mid-afternoon, even if I’m standing up. Diet cola (any brand, pretty much any sub-variety) is my chosen source.
No soda, but we do usually have flavored, unsweetened sparkling beverages (Lacroix, Spindrift).
I have sugar (white, brown, and honey) on hand; olive, vegetable, and sesame oil; brown and white wheat flour, in addition to corn meal and some GF flours like rice and potato; baking soda and baking powder; more spices than I’ll probably ever use; and a good supply of raisins in the freezer. I also keep most of my yeast in the freezer, because I found a 1-pound bag for $6 and it will probably outlive me.
I actually need extra sodium, so having salt on hand is a necessity for me.
Two things that I almost always have on hand are cans of Diet Pepsi, and Tater Tots. I don’t drink coffee, and rarely drink tea. I’m not a milk drinker, so I keep a bag of powdered milk on hand if I need some for cooking.
I have also stocked up on canned fruits, vegetables, and soups in recent months, along with pasta and sauces.
I’m the other way around - no soda in my house, but lots of tea in several varieties. Caffeine is very, very common, and can be delivered in so many ways.
White sugar, brown sugar, icing sugar, Demerara, cane sugar, palm sugar.
AP flour, whole wheat flour, bread flour, corn flour.
Spaghetti, rotini, penne, macaroni, lasagne noodles.
(Old house, large walk in pantry off kitchen!)
No.
We never drink soda, and never had it for our kids when they were in the house. I wonder why anyone would stock something so unnecessary and unhealthy.
I have all of them, but I use salt sparsely and infrequently, flower once in a blue moon, and I never use sugar unless I have a guest who requires it in coffee or tea. In fact, I use baking soda more than any of them because I put a little in my marinara sauce when I make up a batch.
Because they enjoy it. Wine and beer and liquor and cookies and cakes and ice cream (and many other items) are just as unnecessary and not particularly healthy but I’m sure you don’t wonder why people keep those around.
You can take my Coke Zero when you pry it from my cold dead hands.
I have a small amount of everything, but it’s mostly because I went through a big baking phase in the last couple of years watching The British Baking Show and partly just out of habit.
It’s all getting a little stale now though. It’s too hot to bake these days.
I have all of the staples mentioned in the OP and many more:
Coffee
Peanut butter
Butter
Bread
Milk
Garlic
Spices & Herbs galore
Mayo
Mustard
Ketchup
BBQ sauce
Cereal of some sort
Bisquick
Brown sugar
Salad dressing
Eggs
Crackers of some sort
Canned veggies
Soups
Any many others…
We keep some on hand for visitors. Apparently not everyone shares our wine addiction. I’ll have a diet pepsi about once a month.
Speaking of staples, we are always pretty well stocked with beer and wine. And coffee.
No kids in the house, but my mom never had soda in the house either. I just never got hooked on it. Now, it’s too sweet or the sugarless tastes weird. Occasionally I’ll have one if I’m eating fast food, but I usually prefer ice water or coffee.
Do you mind me asking why?
It cuts the acidity of the tomatoes. Use carefully, if using. Too much and it’s absolutely inedible.
Baking soda is also very good for tenderizing stir-fry meats, if you want that take-out Chinese beef/pork/chicken texture. Just let your thinly sliced meat soak in a solution of water and baking soda (maybe about 1/2 tsp per pound to enough water to wet and be able to soak your meat in – I just use enough to be able to get all my meat wet – it needn’t be submerged). Wait 30 minutes, rinse the hell out of it, and continue with your recipe. It really does give the meat that soft, tenderized texture associated with Chinese take-out, but works best on thin slices or strips of meat (which is what you see in Chinese take-out, typically.)