>Meanwhile, the dude with the ice cream truck already charges more on hot days than on regular days, and no one cares.
Not all of them. The two trucks that come to my neighborhood have the same prices all the time. Our weather is more moderate, so that may be a factor. But whether it's 102dF or 60dF, I can always buy $1.50 ice cream from those trucks.
These are almost certainly contract prices for the store. "Just in time" is not compatible with retail grocery stores.
The real parsimonious angle is the cost of refrigeration changes on hot days. Although that means ice cream should be 25% of it's original price during the dead of winter.
And I haven't seen an ice cream truck with a digital price sign. Yet.
But you're currently overpaying for ice cream on days when it isn't hot! You just don't realize it.
Meanwhile, the dude with the ice cream truck already charges more on hot days than on regular days, and no one cares.