Schools have classes that study local history, writing and computer science. It only takes one teacher to bring a whole class of volunteers with her. Teens can also be involved individually as volunteers. Fit it in along the edges. Scanning in a set of photographs is something that can fill a slow afternoon.
Typists can retype a valuable document in a few minutes.
Staff can proofread text to stay busy at desks. Employees on light duty can be trained to scan photographs. Even if a project is assigned a low priority, it will eventually get done. Projects do not need to be massive. In most cases, anything you do will be the largest such project in your community.