A double cab Tacoma has a back seat most owners rarely use and a floor behind it that is nearly impossible to pack. A rear seat delete kit trades the seat for a flat, load-bearing deck, which turns the most awkward space in the truck into the most useful: secure, dry storage inside the cab rather than exposed in the bed.
CargoKits builds those kits for the 3rd generation and 4th generation Tacoma, with the 4th generation version listed for non-hybrid trucks. For the 5th generation 4Runner there are drawer systems and a sleeping platform drawer setup, which puts sliding storage underneath and a flat deck on top long enough to sleep on.
Which one you want comes down to how you use the vehicle. A seat delete is the right answer if the back seat sits empty most of the time and you want that space locked inside the cab. Drawers make more sense in the cargo area of a 4Runner, where the problem is not space but reaching gear without unloading everything stacked on top of it.