I usually plan my menu/ shopping list weekly
A lot of it depends on how much time I have to prepare the meal each day.
Some days I dont get home until late, so I need something that is either quick, can be made in advance or something my wife can handle ( not an insult, she is a self admitted poor cook). Obviously, the more time I have to cook, usually the more extensive the meal will be.
I do try to make at least one new thing each week, so I can expand my arsenal of new meals to add to my repertoire.
Another factor will be if the garden is up and running, that kinda dictates what ill be making , to some extent, assuming I cant store the produce and has to be used fresh and in season.
Sometimes the need to empty the fridge or freezer plays a role in what will cook that week. Especially if we are going away, and need to empty the produce drawers to avoid rot.
There are staples that are always in the house as a " Just in case I get home later than expected", or " I just dont feel like going all out".
Always have Pasta on hand, refried beans and tortillas, pierogi, veggie burgers, Trader Joe's Meatballs, Spaghetti squash, Multiple frozen soups ( Homemade ), Stuff for taco's, Potatoes ( for baked potatoes), Felafel and pita .... So, if I just dont feel like cooking, these are things I can whip up quickly or have my wife prepare for when I get home ( so we dont eat at midnight)
The process starts by me writing the days of the week down and asking Now, just my wife what she is in the mood for. It was more complicate when the kids lived at home. Anyway, this usually leads to a fight ( playful fight, not fisticuffs). Everyone always complains the I can make whatever aaa want, then when I make what I want, they complain they are not in the mood for it.. Catch 22.
The list will also include if we are planning to go out for dinner, if we are traveling or eating at a family members house for an occasion. Once the list is complete, I then go through the meals and list below what I need to prepare them. I'll also do a quick look-see through the fridge, freezer, cupboard to make sure we have the basics, and that I dont buy things we may already have. It is at this time that the fridge gets kind of a quick clean ( leftovers, and crap that got pushed to the back gets chucked).
Our shopping is broken up in two ways. I shop primarily for the ingredients needed for dinners, any specialty store stuff ( Indian, Mexican, Vegetarian/ Health, Asian...). partially cause I know what Im looking for, secondly, cause I truly enjoy shopping, so although I do stick to the list, if something catches my eye as new or something I want to try, ill pick it up too. My wife usually buys the essentials: Salt, oils, snacks, th9ngs to drink, cleaning supplies and stuff like that. Sure there is overlap, but its coordinated so we both dont buy the same thing. She'll also do the Whole Foods and trader joes run, occasionally ill go with her.
In the summer/ fall months we'll take trips out east ( where the farms are, only 20 - 30 minutes away) and hit the local farmers markets just to see what they got, and grab some local roasted corn or a baked potato as a snack.
We do have a relatively well stocked kitchen, is in reality, I could probably come up with a solid weeks worth of dinners without even shopping.
Always have garlic, onions, celery, carrots, potatoes, Multiple canned products like beans, tomatoes, corn, creamed corn. Rolls, bread soups, Veg Chopped meat, veggie burgers, some frozen trader joes prepared meals ( pizzas..), a few pizza crusts all in the freezer, an assortment of pasta sizes and shapes and multiple dried grains, beans, mushrooms. And the basic of all basics as the salt, pepper, spices, oils... Probably more crap too.
So, the simple answer is, yes we plan in advance, but have the capability of thinking/ cooking on the fly if we want to or if the situation calls for it.
Final note: because we have chickens and compost, I dont feel terribly bad if we have some leftovers we dont eat, or things that start to go bad, cause the chickens basically eat anything and everything, so just saves me in feed. If I didn't have the chickens I would likely be more frugal and run a tighter ship