Meal Planning for the Unplannable

So I have tried a few meal planning rotations and love cooking. But I find that since we eat seasonally and closer to our front door it is harder to predict what we will have available in a weeks time or even a couple of days ahead. Maybe we will find a mess of oyster mushrooms or the neighbor drops off a 55 gallon barrel of sweet corn. Now of course preserve to use later is a important tool for spreading out these blessings but when there's a fresh glut I like to base our meals off it. I have a loose system of vague meals that can take a lot of fluctuation of ingredients that I pick from.  Such as Soups and chilies on Saturday, Leftovers on Sunday. Monday we have a meatless bean dinner. Taco Tuesday is more of a general Mexican theme. Wednesday is for rice and a topper. Thursday is not my problem and I make someone else cook. and Friday we grill stuff. This normally works for us but come the hot months it gets busy and I will stop using it.  I want to try changing how we do this and was wondering what others do to help them keep cooking to provide three meals a day, every day, for every mouth at the table. With a pantry of ever changing ingredients.

what a great question.
I also get the glut issue, and I think I address it the same way you do, with "themes" every day. But the themes are very, very broad- one day Turkish with flatbread, one day Japanese/Chinese/Korean with rice or noodles/bread, one day soup.... When I feel like it I'll add in some kind of beans/rice day, Ethiopian day, pancakes with toppings day, etc. It often depends mostly on how I'm feeling.
But I do the "themes" mostly because I hunt online for recipes and it is absolutely overwhelming to search for "recipes with potatoes" or "too many mushrooms", know what I mean? If I can somehow whittle it down a bit ("Chinese mushroom recipes", "mexican potato recipes", etc) it just seems easier to get a handle on things so I can go ahead and whip a full meal together (since now we're really not going out anymore, and we need enough leftovers for lunches too. All our lunches are leftovers, I do not cook lunch, period.)
Recently I've started trying to make a more concerted effort to save the 'keeper' recipes that have become standbys (for example, today is 'Turkish'. which means we'll have whole wheat flatbreads, tabbouleh salad, a bean/soy protein/tomato/pepper stew, and maybe some roasted cauliflower and yogurt sauce). All of these I make so often that I don't need a recipe, but if my daughter wanted to make them I'd like to have it written down-- thinking about what would happen if the beloved sites I originally got them from went off the air (which happens). This  is sort of an ongoing long-term project for me (and an entirely different thread).
But yes, I am ALWAYS searching for what to do with "too much XX".

What dishes can almost anything go into?

chili
curry
other soups and stews
frittata
taco/quesadilla
grain bowl
pasta sauce
salad
stir-fry (and fried rice the next day) or a "skillet" meal
either pickled or served with pickles
baked potatoes