Starting January 18, 1943—the midst of World War II—sliced bread was barred from American bakeries and homes. New baking regulations set by the Office of Price Administration had boosted flour prices, and the government wanted to prevent these costs from getting passed down to the consumer. By banning the use of expensive bread-slicing machines, the government was hoping bakeries could keep their prices low. Officials were also worried about the country's supply of wax paper—and sliced bread required twice as much paraffin wrapping as an unsliced loaf. (It prevented the slices from drying prematurely.)
Wax paper is great! What I think is so funny about this is that to me wax paper feels more premium. I guess it's because it's because plastic is so ubiquitous that despite being an incredible and versatile material, it's also ridiculously mundane.
Your local neighborhood bakery almost certainly still uses wax paper instead of bags. I don't eat much bread these days, but when I do I always just walk down to the bakery and pick out a loaf. It's a million times better than the sugary stuff full of preservatives at the grocery store.
Bakers, bakeries and bakers shops were required by law only to sell their 'national loaves' when they were a day old because stale bread did not cut to waste like fresh bread. Source
[If you can find it, the BBC Timeshift episode 'Bread: A Loaf Affair' mentions this along with a surprisingly interesting modern-ish history of bread in the UK. It's narrated by Tom Baker.]