Neon/Sparkle Jr. Twist Fidget
If "classic fidget" means one toy, it's this. The Tangle has been around since the 1980s — a loop of curved, interlocking segments that twist and click endlessly in one hand, with no battery, no sound, and nothing to lose under the couch. The Jr. is the kid-sized version, small enough to live in a pocket or a backpack pouch. It's the rare fidget a teacher will actually allow, because it's silent and one-handed, so a child can twist it under the desk while still listening. Ours have survived years of being twisted apart and snapped back together.
Builds: quiet self-regulation · fine motor · fidget focus
~$15· See it on Amazon