Especially with the holidays coming up, you can keep your kids busy with arts and crafts. Papercrafts are an inexpensive way to let kids decorate their rooms, or the rest of the house, while its snowing outside.
Keep the education going. Give them homework and projects that can stretch and challenge their minds.
Cooking. If you can't go outside, bring them into the kitchen and teach them about how to correctly use the equipment and utensils.