Great ideas! I usually buy them at Cracker Barrel Restaurants because they have large, pretty ones to choose from and you can get 1 for $2 or 3 for $5. I've made my own in the past, but the plastic ones stand up better while putting groceries in them.
I keep mine folded neatly in a basket in the trunk of my car. After I'm finished putting groceries away, I put the folded empty bags on a table by the front door so I remember to take them back to the car when I go. Some of our grocery stores credit your bill $.05 per bag you bring, sometimes I use 6 or more.