Since I do all my own work, the scrap pile is always close by so I can go through it and use what's in there. I started building my garage addition in the Spring of 2022, and I used a couple boards from that scrap pile over the weekend to create blocking for my ceiling lights. If it's a foot long, or longer, odds are good that it will be used for something.
I also keep a 5 gallon bucket next to my chop saw that I put all my small pieces of wood into. These buckets get stacked in my shop and then are used to start the fire in winter, or whenever we have a fire out on the porch. I probably have a dozen buckets right now, and I'm always adding to them. I also save all the little shavings and splinters from splitting wood in five gallon buckets for the same reason. They dry out quickly and make fantastic kindling to get the fire going.
OSB and Plywood is what I struggle the most with saving. If it sits around too long in my humid climate, it warps and bows on me. I tend to keep the bigger pieces and burn almost all of the smaller pieces.
I also have a garbage bucket full of PVC pipe in a variety of sizes and lengths. It's something that I rarely have any use for, but when I do, it's very nice to have it there. Last time I used it was for a fishing pole next to the pond. I pounded a 4 foot length of 2 inch PVC into the shoreline to hold the pole upright. Then we come back and check it to see if a catfish has taken the bait.
One thing that has become very important to me while living out in the country is how important having "stuff" is, and also in knowing where to look to find it!!!!