Ack, holidays can be a pain when it comes to the weight can't they.
I do think it's important to practice maintaining weight when you are on holiday. I think most people who have weight issues see it as a chance to go mad and eat everything in sight (after all...it is the holiday

), but if you want to get off the dieting bandwagon forever, you need to learn how to maintain whether it's holidays, christmas, whatever.
This is the perfect for you to practice maintenance.
So...smaller portions. Learning how to stop before the meal is finished. Walk places if possible, and above all, see this as a positive challenge...a chance to learn about thinking thin, living like you would do if you were at goal weight IYKWIM.
True maintenance isn't about dieting, nor eating properly when it suits. Nor is it about denying yourself on special occassions. It's about learning to live slim whatever life throws at you.
very best of luck