Lucky Clover

Luck in Terraria is mostly temporary. Potions run out, ladybugs wander off, biome torches have to be placed. This is one of the few sources that just sits there and applies. Keep one anywhere in your inventory or in an opened void bag and it works with no upkeep and no accessory slot spent. A second copy does nothing, so there is no point hoarding them.

Finding one is entirely incidental. Only plain tall grass can drop it, not the flowered kind, and the odds per cut are low enough that nobody sensibly farms for it. What actually happens is you clear grass for seeds or hay during normal play and one falls out. Pocket it and forget about it. Your own luck has no effect on the odds, so drinking a luck potion first will not help.