The easier way!
Please don't trouble yourself. It just as easy as 123!  ^___^

 Step 1 : Place your empty reusable grocery bags in the trolley / shopping cart. 
Pick and put your groceries inside the reusable bags.

Step 2 :  Pay at the cashier and arrange your groceries back inside the reusable bags.
Not only it is easier for you to carry all your groceries  but they are large enough to fit all your items inside. 

Step 3 : Lift the reusable bags straight away into you car's trunk 

Mentalnotes:  You probably need to repeat the same action 2-3 times instead of 10-15 times if you use plastic bags depend on the quantity of your purchase.

Well, as easy as 123 you have successfully save the world! Keep doing this and next time the cashier ask cikjah "do you need plastic bag?"
support the environment by telling them,  "No thanks, I brought my own bags"