Season of calculus, nice!

Gotta mention House of Leaves, too. Another double bookmark book.

A pair of high fidelity earplugs (aka concert earplugs or filtering earplugs). You can get a good non-custom pair for $15–$40, and that’ll work well for the average person for a long time.

They’re excellent for live music, airplanes, and anytime you want the world to be quieter but still need to be able to understand speech. And for music specifically, they can bring the volume level down just enough to be safe without muffling the sound like traditional foam earplugs do. Protect your hearing, kids!