Surtling cores: Farmable from Surtling spawners in the Swamp.
Eggs: Initially purchased from Haldor, then generated by chickens.

Resin/Wood/Stone: Farmable from Greydwarf Nest (via Greydwarves).
Ancient Seed: Farmable from Greydwarf Nest (via Brutes).
Swamp Key: Boss Drop. Only has one use, having more than one is pointless.
Hard Antler: Boss Drop. Only has one use, although having more than one is worthwhile.
Fuling Totem: Farmable from Fuling Berserkers; effectively infinite.
Torn Spirit: Boss Drop.

Fishing bait: Technically only as finite as gold, but annoying to acquire because it only comes from one place (Haldor). Other baits are crafted... from purchased bait plus something else. Fishing is broken, because you are forced to return to Haldor to acquire the ability to continue fishing.

All trophies: Mob drop, thus infinite.
All non-boss Creature drops: Mob drop, thus infinite.

Tree Seeds: Other than beech (and theoretically oak), the drop rate is not high enough to replenish stock via replanting; thus finite.
Plant Seeds: Absolutely infinite, produced 3 at a time via planting 1 "fruit" (ie, end product).