There must be some things that fascinate you. I can't be the only one. There are several that I absolutely love.
1. I love magnets, magnetic clips, magnetic strips, little magnets to put into greeting cards or little boxes, magnets to use to keep things handy.
2. Dowels are another thing for me, particularly small ones, an inch or smaller. There are so many things to make with them. They can even be cut small and used to mix paint. But I use them when I build little houses, holders for hanging things, (attach them to hooks) , help polymer clay dolls stand up, make frames... all day I can think of new uses.
3. Wood of any kind. It is almost impossible for me to let go of any piece of wood. I find scraps handy for making shims, make-shift shelves between two storage containers, little planks to support those flimsy wire shelves, and I use pieces of masonite not only as substrates for painting but as bookends or sturdy dividers between 12x12 cardstock packs or even canvases. And then when it's down to nearly splinters, it can serve as kindling in the fireplace. Sawdust is even good in the garden. (I obviously love trees.)
4. Glass bottles and jars. Baby food jars, wine bottles, mayonnaise containers when they used to be glass. Paint them or not, they are things I love to see in my studio, just being around. Obviously they are handy for uses in painting and to wash brushes, but you can make little terrariums, root plants in them, grow a sweet potato vine, store things, fill them with buttons, baubles and beads!
Actually, containers of any kind. For a long time I saved them all but I had to temper that. There's only so many one person can ever get around to using, not to mention finding space for.
5. Pens, pencils and markers of all kinds. Notebooks. Legal pads. No explanation necessary there.
What are some of yours?