I do it..
But I take what would reasonably be 'breakfast', that fits on a plate and a sideplate (cooked breakfast and a croissant or pastries and fruit) not a tupperware box + plates!
So I just calculate what I could eat for a big breakfast, in a way that means IF there are left overs, they will work for a snack/lunch.
Sooo last time, I think I had two sausages, two bacon and a tomato, mushrooms and toast, and two mini pain aux chocolate.
I ate bacon and tomato and the pain aux choc... I made a butty out of the mushrooms and sausage and had that for lunch later on.
I wouldn't have taken more than I could eat for certain, for a butty later on and if I had eaten the whole lot (feasible back then, not now), I wouldn't have gone back for more for a sneaky theify take out.
If im in a hotel and I have paid for breakfast, I am going to treat myself and have a pretty substantial breakfast. But taking MORE than you can eat, more than anyone would reasonably eat, in order to provide lunch is cheeky as.
The occasions I have done it were all when I was attending a conference at the hotel and knew the buffet lunch would not meet my needs (often all vegan and very high in carbs/pulses).