Social Studies
Discovery Education all subjects K-12
Daily DE for parents to use with students--no login required--features a grade-band appropriate learning activity for every day of the week!
New Visions Social Studies Curriculum You can post these assignments directly to Google Classroom. I always make a copy and adjust them a little before adding them to classroom.
Social Studies Hyperdocs large selection of hyperdocs for both US history and world history.
Tom's Digital Resources : Digital breakoust for US history (these can be a little confusing so I would suggest working through the ones you want to use before assigning).