If you track your nutrition each day, give yourself permission to not get it perfectly right this time (see my blog today on the topic of tracking!).
Before putting anything on your plate, "walk" the buffet to see what's available. You know what the better choices are, so stick to those and be mindful of your portion sizes. Treat yourself to something you wouldn't ordinarily have, but only take a bite or two (you may find it doesn't taste as good as you thought it would, anyway -- we've been training our bodies to reject all that fatty and sugary stuff!).
Most of all, remember what this day is TRULY about, and celebrate Christ's resurrection!! He is Risen! Hallelujah!!