This really is no effort whatsoever. Follow the link to print out the simple and classic calendar. Frame it and mark the days in dry erase marker. Now you have no excuse.
Grab some cookies from Ikea (they come with holes to use as ornaments!) Use icing to write the numbers and ribbon to hang from a tree or branch. Now just eat a cookie a day!
Post-It’s make a great calendar, since each one is already a box. Just decorate one side and write an activity on the sticky side, then stick them to the wall in a grid shape.