I have one behind the drivers and passenger seats from BROG. I'm adding Molle panels and a shelf so I won't need the behind the seat as much.
On the drivers side I have a BROG pouch for surgical gloves. Came in handy this past year. I hardly ever use it now. A spare crappy flashlight and my Grayl water purifier bottle.
On the passenger side, I have a pouch with everyday things like Tums, allergy meds, wet wipes, etc. I also have a water bottle holder that never gets used. Some scissors and a knife.