Don't get me wrong -- I'm not saying either of those things are impossible. People get fitter and thinner all the time, however temporary the change might be. I'm just pointing out that the whole resolution route is, in fact, one of the absolute worst ways to get fit. As I have mentioned before, there's a whole host of reasons losing weight is harder than shitting an entire undigested turkey, ranging from your brain's tendency to want back the pounds you've shed to a horde of little things affecting your weight that you're powerless against. Do you really want to go up against all that crap during the only time of the year when absolutely everyone else is trying to do the same?
Come Monday, this is the line to your nearest 24 Hour Fitness.
As for working out, back in my (slightly) more gym-oriented days, I experienced a fair few January floods of dieters, and I soon noticed that the Resolution Folk tend to have precious little camaraderie. They treat their holy mission to become a better version of themselves with a bloodthirsty fervor usually reserved for knights gearing up for a crusade. At no point will they attempt to enjoy training, and when a week or two goes by and they don't magically turn into Marvel heroes, they tend to lose steam pretty quickly. The few weeks of intense weight-flailing they forced themselves through winds up being more or less meaningless, give or take the occasional hernia or sprained ankle.
So why not just adjust that "I will fix everything about me right now GRAAAH" resolution into a slightly saner one, make a decision to pay slightly more attention to what you eat, and take the stairs instead of the elevator once in a while? All those small things add up, and are a lot easier to keep up in the long run.