Take turns reading out loud to each other.
Borrow joke books from the library and read them out loud to each other.
Make animal shadows on the wall with your kids.
Bake cookies
Drink hot cocoa with lots of marshmallows
Take a walk in the brisk air with the kids and then cuddle under a blanket to warm up when you get home
Take pictures of each other acting silly and upload them to your computer. Use the pictures as wallpaper for your desktop.
Sing silly holiday songs or songs that your kids learn in school.
Browse for freebies on the Internet that you can send away for.

I love getting stuff in the mail!
Send out a bunch of ecards to your friends "just because". Spread some smiles!