Adding to the other commenter, the second stage and the dragon trunk are the only major hardware pieces of falcon 9 that spacex doesn't reuse. The trunk blocks the heat shield on dragon 2 so they have to discard it. It burns up in the atmosphere.

On launches without dragon they instead use fairings that cover the payload. Those fairings are jettisoned and descend under parachute until splashing down in the ocean. They fish them out of the water and reuse them numerous times as well.

SpaceX is also building the starship/superheavy rocket which will have a fully reusable second stage. So ideally it'll launch, land the booster back at the launch site, the 2nd stage goes to orbit, deploys payload (cargo doors attached to the second stage), then the 2nd stage will deorbit and land back at the launch site as well. It's also been chosen by nasa to land humans back on the moon in the coming years. First test launch (no landings yet. Just flight tests) is coming up very soon. Possibly attempt this month but could easily turn into next month.