Blowgun

Keep one anywhere in your inventory and the plants you walk through start shedding ammo. Flowers give the most, plain tall grass gives a trickle, and anything growing in a pot or a planter box counts too. You never have to hold it or fire it for this to work, so one purchase quietly turns every surface run into a resupply run. What drops is ammunition only: you cannot plant it, and the seeds you can plant will not load into the gun.

On seed ammo alone it is a backup at best. It gets interesting once you feed it real darts. In early Hardmode, before a Dart Rifle or a Dart Pistol turns up, loading it with Crystal Darts inside a tunnel is a genuine damage option, because the shards ricochet off the walls and land on the same target again. Out in the open that advantage vanishes and it goes back to being a seed gun.

The Witch Doctor sells it and also carries one himself, which is how he deals with anything that wanders too close to his house.