@Roadrunner53 Absolutely; we make sure we have snacks, entertainment, etc. The first time we traveled with our kids on a long flight we were a party of 6 and paid a ton extra to pick our own seats so we had 3 in front of 3. That way if there were seats being kicked we could configure it that we were in those seats with the kids behind. Fortunately, they do very well and we found it's not a problem. But, we waited until they were 4 and 6 to even put them on a plane the first time.
I know things happen; sometimes a really little one has terrible trouble with their ears and screams. We were on one flight with a family whose two small children (2 and 4 maybe?) were severely motion sick and threw up the whole time. I will say, as a fellow passenger, when the parents are struggling but trying and nice and apologetic I am much more compassionate! We do our best to mitigate against whatever we can, and be attentive to our childrens' needs throughout the trip so that they don't impact others as much as possible.
Sometimes with the grocery store, though, there's not a lot of other options if your kid loses it and you need to buy some essentials. I will be honest, I try very hard not to visibly react when my kids have a public meltdown (thankfully, it isn't often these days!) because sometimes they're after any reaction even if it's negative. That doesn't mean I'm not immensely bothered by it! Unfortunately not everyone has the luxury of a spouse, babysitter, or grandparent if they need to run out to the grocery store. We are very lucky that we live very close to work, so almost all of our shopping is done at lunch time without kids. We grocery shop without kids whenever possible; it's generally quicker and cheaper that way.
We had a few issues when our kids were younger in grocery stores with meltdowns and temper tantrums. Our response was certainly not to reward that behavior with candy or other treats to get them to calm down immediately. We generally tried to get them to stop by talking to them and if that didn't work we then "dealt with it" in private. Giving in and letting them have a treat will help short term but it will train them to repeat the behavior in the future. There are lots of opinions on this and no one option will work with every kid. This worked pretty well for us because although all our kids tried the temper tantrum thing a couple times they stopped pretty quickly when it didn't work.
Note that I do think preemptively keeping them happy with snacks, toys, games, etc is a great idea and can help considerably. We just didn't use those as a reward for bad behavior. They got those things preemptively or after they calmed down.