I'm looking into picking up a 'drag matt' its a combination of a drag matt and a shooting matt. (Its in the royal mail, haven't trialled it)
Walk onto the firing point with the bag, unzip it, unfold the mat and anything I need is ready to hand in the internal pockets along with the rifle.
When your finish pack everything up and walk to you car/ next event
Any other non essential bits stay in the car in a plastic toolbox until I need them. (But I typically have the car at the back of the firing point)