It is different in America, of course. Regulations vary from country to country. And I know, from farm folks in the family that "sell-by" dates on dairy means the product within is good for a week after that printed date. They (rightly) don't expect you to consume that whole gallon of milk the same day you buy it! And if unopened, it may be good afterwards, it's up to you to "sniff test."

Eggs that you are unsure of you can always test for freshness, that has been discussed here in other threads.

And inert things, like baking soda and baking powder, basically those dates mean very little. I have used baking powder over a year after it's use by date, and the cake rose just fine!