So rather then wasting just your own time, waste the time of everyone in the queue behind you and the cashiers too ? I'd rather spend time organizing in my own house than in public + wasting other peoples time.
Some people can do it just as fast as it's given to them, meaning it's done before they ask for the card.
Mine always do , I can barely have 3 bottles of beer in them cheap rubbish plastic bags without them breaking when cycling somewhere, I wasted 2 bottles of beer once out of 3 this way: Bag broke, fell and broke 2/3rds of the content .
Must be the way you pack then. I can get away with a couple of bottles of fizz, some tins and flour/marg/bananas etc. filling it to the brim and struggling to carry it without it breaking. The bounciness of the bag when it's that heavy is odd however...