Just a small life hack here...I purchased a D-ring for rock climbing and tossed it in my grocery getter. I take it in with me when I shop, and as I load bags into the car, I loop them into the D-ring. That way when I get home, its just like a handle for all of the groceries. Keeps my strong hand free.
my advice to you would be: carry at all times...even at home.
and when the pistol is not on your person...invest in a good safe in which to keep it locked up.
As long as you are the driver, and you don't get out of the car at school, then you are allowed to have the gun. This gets easier on July 1st of this yr.
If I were to use a D-ring for bags (I rarely buy enough stuff to even need a bag) I think it would be better to loop the D-ring through while still in the store, rather then as you load them in the car. Then you aren't standing longer at your car in the parking lot then you need to.
I wait because I like to clip things in order of temperature...(keep all of the cold stuff together). Then I make sure the fragile stuff is on it's own d-ring.