The next few weekends should be about the right time for putting these down. Straw is the popular material. Another area to check now is storage of garden chemicals, including pesticides and fertilizers. If storing them indoors, place them up and away from children and pets. Make sure the containers are sound.
Adequate ventilation is also important.
Dry materials, such as fertilizers, may not be damaged from freezing but do not tolerate moisture. Check to see the package is sealed tightly to protect the contents. Finally, don't forget about equipment that was not ready for winter when the snow hit. Hoses should be drained of water to avoid damage. Check the owners manual or the implement dealer for the best way to prepare and store the lawn mower.