How long has it been since you have flown frequently? No one brings grocery bags any more. Watch what you wish for. Those bag sizers are absolutely set there as revenue generators, and they tend to shrink over time.
I agree with Organic Panic.
See my post below your’s.
I fly every two weeks. The grocery bag lady is on every flight. It is usually an older woman with a huge wool sweater, unkempt clothing, and poor hygeine. I imagine the grocery bag people read a budget travel blog that recommends bringing your own food. Blankets, sweaters, scarves, pillows, food, all billowing out of bags.