The coffee with lots of light cream is pretty much my Number 1 "food thing" - but I live on it, so I can't call it a "guilty pleasure".
I'd say my guilty pleasure is Klondike bars with Heath Bar ice cream. I'll go on a two-day Klondike bar binge every couple of years. 8 bars in the package (share two with family members and it leaves 6 - 1 for dinner on the evening of the evil purchase, breakfast, lunch, dinner, snack and breakfast again.