Yes, people plan ahead. Perhaps not all of them have five-year plans written out, but they often have a vision of what is to come. The future. If you're writing about characters, it's worth asking whether they are thinking ahead, and how. And if they aren't thinking ahead, why aren't they?
I've heard it said that in science fiction, people don't do a lot of thinking about the future. It's probably true, and likely happens because people in science fiction are often in the future, so the author hasn't done a lot of thinking about the future of the future. I have a feeling that "future" in this context refers to grand visions of new technologies or changes in society. People in science fiction do tend to have a pretty clear idea of what bad thing will happen if they don't get their job done, or what will happen if the Romulans invade, etc.
We think ahead in different ranges. What to do for the next few minutes, what's on the schedule in an hour, our plans for next week, during the next year, when I grow up, or what the next century or millennium might involve.
Things that are predictable and assured tend not to be given a lot of thought. Unless you're starving, you don't have to give a ton of thought to where your next meal is coming from. You'll generally give it some more thought if you're responsible for cooking it yourself. And if you enjoy cooking, that might inspire you to get some more dramatic ideas. If you're just showing up at the usual place for dinner, and eating the usual things, you might save your thought for other more important concerns.
If you have a few things to do, you might think ahead to plan the order in which to accomplish them. If you have a lot of things to do, you might make a list because it's too much for your brain to handle at any one time. Your list becomes your place for thinking ahead, while you keep your mental focus on the tasks at hand.
Stress is one reason why people do less thinking ahead. A to-do list reduces the need to think ahead more than a little bit. The more extreme the stress, the less thinking ahead you'll do. Say you're in a sword fight; you are going to be thinking about the next parry, the next move to stay safe. You won't be thinking about where to go to lunch afterward, because if you do, you're likely to lose. If you're climbing a rock wall, you have to think about where to put your hand next, where to put your foot next, and where to anchor yourself. Distraction leads to a fall.
This is a pretty good reason why you wouldn't want to put anything but short-term planning ahead into a fight scene, or a flight scene.
I remember when my first child was a baby. I experienced a strange time distortion, in which a period of ten minutes could feel interminable, but weeks would fly by. This was an effect of the stress of learning to deal with my baby's needs. When a child is crying and you are trying to console them, heal them, or otherwise find the answer to fixing their situation, there's no room in your head to envision even the remainder of the day. Only in retrospect do you have any sense of the way that time is passing.
Be careful with the medium- to long-term planning in baby care scenes, too.
Other things can cause a suspension of planning. Sending out a message and waiting for the response can cause someone to stop planning ahead, because they won't be able to act on whatever the message was about until they hear the answer.
Uncertainty can cause a person to stop planning. Say a character loses their job; the lack of income can cause them to suspend existing plans that required money, and to stop planning such things in favor of planning how to get a new job!
From my own life, I think about sending out stories on submission. I tend to stop planning sequels for a story that's on submission, particularly if I'm uncertain about whether it will sell. Some authors fall prey to the temptation to stop planning ahead altogether, but you can't give into that. Don't stop writing - if you feel too uncertain about that path, just plan and write other things.
I'm sure there is a great deal of individual variation in the way people plan. Some people are constantly planning; others just go with the flow and plan when necessary. People who are natural planners may get very frustrated when they encounter uncertainty. Being able to start planning again will be a relief for them. Some people may resist any need to plan, and figure that reacting to things as they come will be the best approach.
It's something to think about.