One thing you could do right now (rather than starting a "full-blown diet") is start practicing
by gradually cutting out certain things. If you go to a holiday party and there's a plateful of very yummy looking cookies, have one or two and say "no" to more. If you go out to eat, order a salad instead of a burger -- or maybe a chicken sandwich. The next time you reach for a non-diet soda, have a glass of water instead. Eat an apple (or other fruit) that you wouldn't normally have. This doesn't need to be every day -- just now and then. I can almost guarantee that the more GOOD choices you make, the easier it will be to make more AND it will be much easier to go "full-blown" when you decide to. That's how I started by the way -- by gradually making healthy changes (3 Cokes a day instead of 4, etc.)
When you're shopping for holiday gifts, park farther away from the mall than you normally would. LOL, you might have to ANYWAY considering how close we are to Christmas. But instead of saying, "Oh crud, I'm 3 miles away!" look at it as a positive thing -- think about the extra calories you'll burn on the hike to the mall!
I always say starting gradually is a huge help when you're starting out. You'll get in the groove of saying "no" to certain things and finding healthy alternatives for what you'd normally eat.
And who knows, you just MIGHT lose a pound or two before you even start!
And that would be a GREAT holiday gift to yourself, right?