"Buying the cow"
I'm disappointed every time I read a comment about "why would he buy the cow when he gets the milk for free" when it comes to a couple living together before marriage. Like we should be needing to entice a man with a promise of more to come in order to keep him interested enough to want to marry us. Personally, I would never marry a man I never lived with. You see, this period isn't only about "convincing" a man that you are worth that ring, but also about vetting a future life partner. Does he do his fair share? Does he get on your nerves when you live with him all day? How does he deal with a disagreement, when he can't just drive off to his place to cool off for a couple of days?
This might sound corny, I know, but the right man will love living with you and will want to lock it down to ensure you are his forever. A man that once you're living together takes you for granted is basically not the man you want to marry!
I would draw the line at buying a house/having children before marriage, because these things make it harder to leave a relationship and they are arguably a longer term commitment than some marriages.