Everything a Hard Mode death takes is held by the Grim Reaper, reachable from Settings. You can buy it all back with credits: the cost is the total shop value of what you lost, at 5,000,000 gp per credit, rounded up, minimum 1 credit. It's all or nothing — you can't reclaim individual items. Reclaimed items (including any charges left in a scythe, trident, blowpipe or shardglass weapon) go straight to your bank.
The Reaper only ever holds one death. If you die in Hard Mode again before reclaiming, whatever was stashed is lost forever and replaced by the new death's items.