Building houses that are properly insulated would help far more since people wouldn't have to use heating and cooling as often, yet that doesn't seem to be a thing that builders are actually doing. I'm an Aussie living in California in a house built in the 1960s, and it's better insulated than an Aussie house built in the 2010s.
In any case, updating food packaging to include an environmental score isn't a bad idea. Hopefully it'd work out better than the health score, which is still entirely voluntary and doesn't always make sense.