One or two won't hurt, but when it comes to crap like Big Macs, I'd start thinking about not only the
calories, but what's actually in there. There's a whole bunch of processed stuff in there, and they're re-heated for hours sometimes. Really no
nutrition value at all

.
Sometimes when I cheat, I try and make it up by downing two tasty V8's and some All-Bran cereal to get some
nutrition in there somewhere.