I've written a sort article about what a programmer can do during Christmas holidays [https://medium.com/@shiroginne/%D1%87%D0%B5%D0%BC-%D0%B7%D0%B0%D0%BD%D1%8F%D1%82%D1%8C%D1%81%D1%8F-%D0%BF%D1%80%D0%BE%D0%B3%D1%80%