Our favourite bread has been thinflated. I wonder if I'm at the point where I should start baking my own...

What's thinflation? Search results are coming up pretty bare here...

You buy a box of cereal at 450 grams for $10. Next week, it's 400 grams, still $10.

it's been going on for decades.

people shop on price, not price per gram, so when you gotta raise prices one company doing 450 grams for $11 and another doing 400 grams for $10, the $10 will win.

I'd rather have the $11 and have to buy it less often

Yep, this!

And after some time with the new smaller format, since they can't do that forever (can't sell baguettes as loafs), they can come up with a "new! bonus pack! 50 more grams for the same price" which they can keep for a few months, then go back with the previous 450g packaging and then increase the price...

yeah