What I like to do is go on a nature hike. Even though I hate the cold, I do feel invigorated by being outside, particularly when there is a guide sharing some insight into what that particular object or twig on the trail represents. Plus some will give you a scarf to wear -- at least for the group picture to commemorate the First Day Hike.
The concept was created by America's State Parks, though the National Park Service now also offers New Year's Walks, increasing the odds of finding a park near you that will inspire you to start 2019 on the right foot. (Do be sure to ascertain the program is still on even if the government shutdown persists).
Of course, the weather doesn't always cooperate. Last year, we did not get to go because it was extremely cold, and some of the hikes were canceled. Even so, according to America's State Parks' site, there were close to 55,000 hikers out for such event last year.
Sometimes the best things in life really are free.