Here's a strange subject

[HYHYBT]

It actually stems from sit down restaurant's policy to ban any outside food or drink from the premises. The idea is that if brought food from somewhere else, you won't be buying as much from them. Sound policy, and standalone fast food places have adopted it themselves, though usually only if you're staying.

It's a liability-and-reputation thing, and the only time I remember it really being an issue was when people wanted to bring their own cakes for a birthday party. It wasn't a matter of "if they bring their own we can't sell them one" because cake was included in the price of the party: who knows who made that cake or how it was handled but if a crowd of 8 year olds gets food poisoning at McDonald's then guess who gets the blame?