Although I believe that we should reduce the amount we waste, I don't think it'll be entirely possible to control. I'm sure companies and such buy, from your example, a lot of milk with the expectation that they'll sell it all and it's unfortunate when they do not.
In terms of food, I really do think restaurants and such should think of a good method that will allow them to get rid of the food they no longer need, but is still edible even though it's close to or slightly past it's expiry date and reduce the amount of waste they produce.
For example, I watched this episode of cheap skates where a woman literally went out every evening to look into the bins of high-end grocery stores to retrieve food for free so that she could eat it, so I think it would be a good idea if restaurants just left their food behind their building or something so that the homeless and/or those that want free food can just come by a pick it up to take away? I don't see why they'd have any reason to complain, it's better people took it rather than letting it rot.
Here is the vid:
[video="youtube;11c4LRomkSo"]https://www.youtube.com/watch?v=11c4LRomkSo[/video]