My neighbour occasionally borrows cooking ingredients. I occasionally borrow tools.
I wouldn’t expect there to be as much borrowing of cooking ingredients today when compared to the 60s or earlier because there is greater use of prepared foods today.
Classic Charles Addams cartoon: The mother of Addam’s family (Morticia in the TV show, never named in the comics), at her neighbor’s door, asking, “Can I borrow a cup of cyanide?”
My sister once had to do this, back when she was in high school (so, perhaps 25 years ago), with humorous results. I can’t remember what she was making, but she needed a couple of eggs. So she went across the street to our neighbor H. Now, H spoke English fluently, but his first language was Spanish. And since my sister was studying Spanish in school at the time, he insisted that she speak to him only in that language, to give her practice. So she rings the doorbell, and says “H, I need two…” H responds “En espanol! En espanol!”. So she starts over “Necessito dos…” She makes her fingers into a little egg shape, but she can’t remember the word “huevos”. “Necessito dos pollitos”. “Dos… pollitos?” “Si, si!” She holds her elbows out and flaps the Chicken Dance “Pollo,” then repeats the egg shape with her fingers, “pollitos!”. “Pollo, pollitos.”
For years afterwards, whenever H saw her, he would say “Pollo, pollitos”, and crack up laughing.
Our pot-smoking neighbors in an apartment we lived in once came over to borrow a 9x13 pan, of all things. Apparently they’d bought some instant pasta thing and didn’t realize until they got home that they were supposed to cook it in, like, an actual pan.
So we loaned it to them and then they offered us some of the finished product after it was done. We said, thanks but we’ll just take the pan back, if you don’t mind. 
Happens all the time on our little dead end street.
But then we do have a bit of a time warpage on our block. Had a coworker drop by and, seeing the kids in their Big Wheels with their sidewalk chalk, and me taking a break from my manual ‘reel’ mower with a pitcher of lemonade, asked she’d taken a wrong turn into the Eisenhower Era.
I got a stick of butter from the neighbor to the left of me this summer and a teaspoon of baking soda from the neighbor to the right of me yesterday. I do the same for them. We have a couple grocery stores < a mile away but why bother.
I do this in my neighborhood in Washington, DC. Usually, I’ll text my neighbors and asks if they the ingredient I need and they do the same. We also borrow each other’s tools and feel free to just grab them and tell them about it later.
Yeah, I’ve had neighbours drop by for eggs and tinfoil, for example: it happens. No big deal.
I guess they did not tell you that it was to seal a leak.
We do it with our next door neighbors (Long Beach, California) reasonably often. Most recently on Thanksgiving morning, when it was discovered that I’d deviled all of our eggs - not realizing I’d later need two for something else on the menu.
Happens all the time in my neighbourhood.
Yesterday, we borrowed some green onions.
On Tuesday, another neighbour was looking for marshmallows.
Cartons or bags of milk, cup of sugar, stick of butter, limes for drinks, etc…
I don’t talk to my neighbors, except for my sister who lives a few houses down, and we do occasionally borrow ingredients, but we also live walking distance from a grocery store and a pharmacy. But why not?
In early 1986, I was called out of class. My mother had gone to a neighbor’s flat to borrow some ingredients and forgotten to grab her keys. It was a working day and there were several supermarkets within 100 yards (seriously, two in the same block and another across one street), but she’d had surgery recently and still didn’t leave the building.
It was the one time I got to skip class during all of HS.
I’ve had a neighbor ask whether she could have some oil, way early in the morning on a Sunday (the local supermarket opens, but pretty late and for only two hours). No prob, I handed her the bottle and she brought it back after putting some in the pan.
No direct payback in any case, it’s generally assumed that since everybody helps everybody else in small ways, eventually it all evens out.
When I lived with my parents in the 70s and 80s, happened all the time.
One neighbour in particular used to abuse the system, basically to be nosey. When I had a GF over and my parents were away, I could bet that, more often than not, this neighbour would just happen by for an egg or a cup of sugar.
Happens all the time at the small community where my summer cabin is. A neighbour sends the kids over to borrow some curry or an egg or a tomato or a cup of something. If they remember they replace with an entire bottle or a dozen eggs or a bag of sugar the next time they go to town to shop, but usually things even out so no one makes a big deal of replacing what was borrowed. We all share our homegrown crops too, since you can only eat so many raspberries or zucchinis at once.
In the city there is a grocery store 2 minutes away, easy enough to go buy the missing ingredient so no borrowing necessary.
Perhaps, mom and dad set her up to keep tabs on you!
When I was a kid, it happened quite frequently. But we lived ten miles at least to the nearest grocery store (they didn’t have 7-11 or White Hen back then). Now? Never. But I have everything within a mile or so now.
Happens a lot in our little valley. Of course, we also share meals and cooking, especially this time of the year. In fact, my closest neighbors (who are also my closest friends which is rather odd) also share house keys with me. If, for example, I needed a cup of milk right now and I didn’t want to drive up to the highway, I could walk next door and if they weren’t home, I would borrow a cup of milk. I’d let them know, and wouldn’t let their cats out, and I usually will bring something in exchange (like a bottle of wine or something). I can’t tell you how it feels to have a community like this. When you open your refrigerator and find other people’s leftovers there because they know you are still (technically) a bachelor, or if I find a six pack of beer with a note saying, “Thanks for the flour and sugar,” well that is really hard to believe in this day and age.
I remember it happening often as a kid in the 70s and 80s. We’d borrow common baking ingredients from neighbors and they’d borrow from us. We were in the burbs of a couple Midwestern cities. It made sense in a world without 24 hour grocery stores, ATM machines, and grocery stores didn’t take credit cards. Writing a check for $100 of weekly groceries was ok, but you’re not writing a check for a crate of eggs or a gallon of milk. Also, driving a rear wheel drive car in the snow wasn’t something you wanted to do, the streets weren’t often plowed first thing in the am.
I’d find it odd if a neighbor asked me for something in my current apartment building. It’s mainly studio apartments with small kitchens. I doubt that many of my neighbors do any serious cooking. Also, since I live alone I don’t actually have sugar or flour in my apartment since I never bake. I’ve got a few sugar packs for friends if they want it with coffee.
Heh, that never even occurred to me. 
Though my impression was that my parents thought this neighbour was nosy, too.