Does Lady Chance like to play games? 4 adults is the perfect number to play a lot of games. You might try Cranium or another more interesting-type game, and Baby Kate might even be able to “help” (depending on her age).
Do you enjoy your family, especially the in-laws? It might be fun to put together some little (or big, if you’d like) token of appreciation for having a great family. You could make/put together little gifts for each person there, to say that one of the things you’re thankful for is your excellent wife and her cool family. I’m thinking, maybe a photo of you guys that you love, nicely framed with a note, something like that. That will help make it memorable and set a tone of this being a special and enjoyable Thanksgiving.
The games thing is a great idea – in my family, we play games like crazy. Pictionary is a real favorite, but Hearts and Taboo and Nertz and Spoons and others are always fun for all ages.
Consider volunteering Thanksgiving morning – nothing like doing good to get you in the spirit of the day.
Pack up after the meal and go for a long walk somewhere beautiful – the beach or a river if you’re near one; the mountains, if you can; woods, whatever. Find and outdoor firepit and build a bonfire and bring a thermous of cocoa or cider.
Before or after the meal, go decorate a tree for wildlife. String popcorn and maybe cranberries or raisins on thread and wind them on the branches. Hang pinecones LIGHTLY coated in peanut butter and rolled in birdseed. Wedge dried corn into the crooks of branches. Put suet in grapefruit or orange halves and hang them or set them on the branches. Lots of birds seek out fruit, so put out wedged oranges, lemons, or apples. Sprinkle birdseed around. Throw out some bread. Whatever. It can look really pretty and the animals love it, naturally.