Late to this thread.
I too carry a multitude of reusable bags in my trunk. HATE when I forget to bring them in the store - I cringe at every plastic bag the cashier tries to give me - also, CRINGE when they try to just put a couple things in each bag - and therefore want me walking out with 10 plastic bags for what would fit in 2 paper bags! Ugh. Cashiers often use the plastic bags like water - endlessly!
I have washed my reusable bags. They actually normally wash up quite nice - right in the washing machine! Not after every use.