Local content does not apply to all subjects, but even adding one local picture can increase students' connection with the material. History is ripe for adding local content. Busisness is another where a local busisness example could be substituted for one in the textbook. Other subjects may be difficult to find a local connection, but it can never hurt to look. Even an event taking place overseas may have a local connection.
Local archives and special collections have often put many interesting documents and pictures online. Even adding a picture of a local soldier in a history book will be more compelling to students than a general one. Check local online repositories.
Of course, pictures and other documents can also be obtained from local archives in person. Normally, there is not money or time to put everything online, so there is much that is only accessible in person. However, archivists are very knowledgeable about their own collections and will likely be able to track down what you are looking for, if they have it.
Sometimes in checking local online collections, something more general, but interesting might be found. That was the case for Corvallis, OR. Nothing local was found, but some interesting documents were found. Below is a map of the universities that American and Canadian students, born to Japanese parents, attended from 1941-1943. Below that is a map of The Empire of Japan in 1942. It is interesting to note that it is from a German book, so it is labeled the Japanese Reich.
National (and local) digital collections can be another good place to find local content. In the Library of Congress collections, the user can search on WWII and then narrow down by location. In the Northwest, much of the contribution on the Homefront involved agriculture. For example, below is a picture from Yakima County of women sorting the hops.
Women on the Homefront participated in every part of the country. Below is a picture from Yakima County of women sorting the hops.
Local content does not necessarily apply. Can local content be added to a book about online learning?
There may be MOOCs on something local to your area. For example, in Virgina, this MOOC on Patrick Henry or this MOOC on Thomas Jefferson would be local content that might spark a student's interest in online education.