Very simple:
Perform 3, 15 minute high intensity workouts per week. Do bodyweight if you don't have weights. Pushups, pullups, squats (avoid situps)
Make sure you stick to your diet. Use the holiday meal as a cheat meal. However, most people consume 2-3 times their normal amount of food during just one holiday meal. So, keep your portions small.
I allow myself about 3-4 cheat meals per week, so social situations are no problem.