My daughter will probably take a packed lunch just about every day this year because she rarely likes more than one item on the menu that is being served on a particular day. I know that I can pack her lunch cheaper than she can buy it - especially if she's going to throw away half of it and not eat it!
Now that my son is in middle school, he's finding that they offer more choices so he wants to eat there. For the most part he'll probably pack his lunch but there's days, like today, where stuffed crust pizza at school will win out.