These were traditionally days of penance, fasting, and praying litanies. If you are in good health, please remember to observe these days. Again, while not required until penalty of sin by the Holy Church, these days can still be observed. I am greatly encouraging them. For more information on Rogation days, see the links in my post entitled Rogation Day: Fasting and Penance. I greatly encourage people to observe these days and spend time praying the Litany of Saints not only for a bountiful harvest but also for mercy and repentance.
The New Liturgical Movement also has a post on the topic.