Fortunately for me, I sub for many teachers who invest in Brainquest cards. They come in a small package and a few are designed for each grade level. Each card contains a ton of questions related to math, geography, history, grammar, science, etc. The cards also have answers on the back, so they are good resource to have.
They are convenient, contain good information, and they are easy to use. They are really helpful for resourceful substitutes because you can use them in all sorts of ways. Over the years, I have used them to give a quick mental challenge to students as the clock winds down for the end of the day, and I've also allowed students to sit in pairs and use them as a free time activity. Just recently, I took the box of Brainquest cards with me in the hallway and asked students questions to keep them occupied while we waited during a restroom break and for another class to clear out of the art room. It's easy to make the questions a game. The kids always respond really well to Brainquest because they questions are usually accessible, things kids know or are interested to learn.
If you haven't seen them, try them out for your grade level (they have products for preschool through seventh grade). They have a website for students to answer questions online. I believe they also make workbooks and boardgames. Nevertheless, I like the quick simplicity and engagement you get from the cards. They've been lifesavers several times.