TryScience, produced by the New York Hall of Science, offers a nice collection of online and offline science activities for elementary school students. On TryScience you will dozens of activities arranged by topic. The offline activities are hands-on activities like wind mapping with bubbles and building tin foil boats. The most of the online activities, like Catch the Wave, have an offline activity that you can use to teach the same concepts found in the online version.
Applications for Education
The next time that you are looking for an elementary school science activity that you can use with or without Internet access, take a look through TryScience's gallery of activities.