Sugar cookies are one of the two great fallback cookie recipes out there. (The other being chocolate chip cookies.) Sugar cookies are great because you can just do simple ones where you drop them on the baking sheet or you can make rolled ones that you cut into shapes.
Sugar cookies are a great basic cookie and can be decorated for any holiday. Personally, I like colored sprinkles (pink and red for Valentine's Day, green for St. Patrick's Day, pastels for Easter...you get the idea) because I feel they add just enough festiveness without overloading on the sugar. Another common topping is icing, but I find that it usually too sweet for my tastes. You could also use icing to hold candy decorations in place.
Plain, undecorated sugar cookies are also great for dipping into coffee or hot cocoa. Or for slathering with your favorite ice cream and making an ice cream sandwich.