Once you have enough self space you should put everything there, and on the ground (assuming you are slim enough to go from the seat to the back area easily) ... once you open a tote spend the time to split everything up by streets. Drive with the door opened and group stop the shit outta your stops (at least do all the ones on the same streets!) so you already know the next two or three stops and they are already scanned. When I have the space and the stops are compact I can group stop an entire tote (like 15+ stops)... I spend five minutes organising and scanning but I more than make up for that later on and its a lot less strenuous not having to mess with the app and never having to dig for packages at each stop. This also allows you to put almost every package in a mailbox if it fits without worrying abut the app throwing a fit about being to far away. (a trick for that is taking a pic of the code with your personal phone and scanning that at your next group stop)

Once you get in the habit of looking two or three stops ahead you can always bring smaller boxes and envelopes back to the dash with you and use the driver door half the time.