Two days is perfectly fine, especially if it’s still sealed. You should be able to use dairy products up to a week after the "sell by" date. If they’ve been opened, then you should use it up within a week regardless of what the "sell by" date is.

These are what the three codes mean:
Sell by Don’t buy the product after this date. This is the "expiration date."
Best if used by Flavor or quality is best by this date but the product is still edible thereafter.
Use by This is the last day that the manufacturer vouches for the product’s quality.

I’m curious about this too- I have a quart of buttermilk that has an expiration date of…well, let’s just say it was still very cold in Chicago (which it definitely isn’t anymore!)…I kinda forgot about it, so I gingerly sniffed it…it smelled fine. Had that mild yogurt smell, like sour cream, and there’s no lumps or anything. I’m too chicken to use it so far, but if it smells okay, is it okay?

I should just but powdered buttermilk. I don’t use it often enough to keep the real stuff around.