A single day won't sabotage you unless you really, really, really, overdo it. The way you word your question, I wonder if you're still in that "diet" mentality where you deny yourself certain things because they're "fattening". "Cheating" implies that there are some things that make you "lose" and others that make you "win".
What I do on special occasions is set myself to maintenance, and allow myself to go up to the top of my maintenance range. I won't necessarily be losing anything, but I won't be sabotaging my efforts.
Healthy living isn't about denial and stress on special occasions; it's about enjoying life when you're presented with fun opportunities. Enjoy your family gathering, make smart decisions, and avoid the scale for a couple of days in case you get a sodium overdose. :)
Writer, mother, wife, and breadwinner. I love to run, but running doesn't love me, so I'm switching to my low-impact bike.
I'm not pregnant, just fat: My blog. fatnotpregnant.blogspot.com/
| current weight: 186.4