Also available on the Steam Workshop:

This mod adds Ender Chests to your game!

Ender Chests work like the same-named chests in Minecraft. You can put in items or take out items, and it stores them between runs.

Ender Chests have a small chance to replace regular chests, and appear more in secret rooms. If you have the Chest Enchanter trinket, then you can find them with a higher chance.
You can only take out or put in one item per chest, though! This creates a sorta dillema; if you have a good item that you might need in another run, you can make your current run worse, but future you will be happy for putting that item in.

Chest inventories are locked by gamemode, so you can't get items you put in Greed mode in Hard mode, and vice versa. You also need a key to access each one.

You can select an item by using arrow keys and your enter/space key to select an item. If you try to select while you don't have an item selected, then it'll cancel out and lock the chest back (however, you don't need another key to open it).

This mod is highly unbalanced. I am fully aware of this. As unbalanced as it is, I feel like its worth the imbalance for a bit of fun once in a while due to relying on past you's ruined runs.
Please report any issues, as I haven't had the time to properly test everything!