There are currently death chest mods, but I wanted to create one without the need for a modloader so I made this death barrel data pack. This data pack spawns 0-2 barrels on death depending on how many are needed to store your entire inventory. When you break a death barrel, it only drops your inventory, so no free barrels just for dying. Regular barrels still drop normally.
Please enjoy, it took me about 6 hours to figure out how to make this

NOTE:

• The keepInventory gamerule must be set to true. You can do that with /gamerule keepInventory true
  
• Players will not lose their EXP on death