All the salt in the sea.
Evaporate every ocean and about 4.7 × 10¹⁹ kg of dissolved salt is left behind. Spread that pile of rock salt evenly over dry land, and how deep does the layer get?
Ocean mass (≈ 1.35 × 10²¹ kg) and average salinity (≈ 3.5% by mass) are both long-run averages — real salinity varies by location and depth, and published ocean-mass estimates vary slightly by source; multiplying the two gives the total dissolved salt mass used above, ≈ 4.725 × 10¹⁹ kg. Spreading it as rock salt (halite, ρ ≈ 2,170 kg/m³) is also a simplification — real evaporite deposits vary in composition and packed density. Spread over every scrap of the world's dry land (≈ 1.49 × 10⁸ km²), this works out to about 146 m, which lines up with the commonly cited trivia claim that all the ocean's salt would blanket the continents roughly 500 feet deep. A separate picker row isn't included below — the four buttons above already are the "try a real value" mechanism this page needs. See the USGS on ocean salinity or Wikipedia's Seawater article for the source figures.