"Кушать" is the only choice for very polite speech. Consider these very old and extortedly polite forms:

"Кушайте, барин!"
"Кушать подано!"

You cannot use "есть" above. On the other hand, as already mentioned, this word should not be used concerning yourself, unless it should concern your dearest self: "не видишь, мы кушаем!" (from a movie, a VIP talking about himself in plural).