I received an unexpected comp room for December and decided to book two week nights. I'm staying at Oceans in AC. What is there to do in December?

We aren't gamblers and are staying for the fun of it. We're planning on having a few nice meals at the Casino. Avoiding the rest of AC entirely. Thinking of visiting:

Asbury on way to or from AC to visit the pinball museum
Seaside on way to/from just to see the place (arcades, pizza, etc). Go often in Summer
Ocean City? Big unknown for me. Visited once in Summer, liked it, but IDK what it's like in the off season
Wildwood. I've heard so much about it, but I've never been south of Ocean City

I fully understand that the shore is dead in the Winter. That's kind of the appeal, I'd love a different perspective of it all.

Well if you travel to wildwood, I suggest Mudhen brewery for lunch/happy hr. Food and beers are on point, they also have a full bar if you don't like beer.
You could always take a ride on the cape may lewis ferry and enjoy the shops in DE.
As far as AC goes, Bass Pro is there.

Atlantic City has a lot of options for food and drink, not much else if your not a gambler. Ocean City and Wildwood are mostly seasonal communities, you can go walk the boardwalks but most shops are closed for winter. Cape May is a beautiful Victorian town, the Washington Street Mall is a nice walk. You could catch a sunset at Sunset Beach, see the remains of the concrete ship, climb the lookout tower or climb the Cape May Point Lighthouse. Cape May Point State Park has some nature trails and a birdwatching platform. If you are into beer or wine there are a bunch of breweries and wineries (a couple distilleries too) in the Atlantic/Cape May county area. Historic Cold Spring Village in Lower Twp has the states only non-profit brewery and the village is cute.
You can cruise down ocean drive through the beach towns. Lucy the Elephant is worth looking at once in your life - the butt-hole window used to be the bathroom. About an hour west of AC you could check out Batsto Village, it’s a historic village frequented by the Jersey Devil. If you have a 4WD there are some trails through the pine barrens, don’t try to take a selfie with a timber rattler snake.