Everyone has sich great ideas, so I will just list a few of my own, (my boys are 10, 8 and 3)
Chores: one does chores while I work 1on1
Manipulatives: Cuisinaire rods and legos, and counting frogs, buttons...... Let them go, no planning, and lots of learning.
Books: one pile, one couch, one boy, an hour of learning!
Art: find an art book with easy crafts that they can follow the directions too. The libraries have tons of them. Clay, Sculpey, stickers, paper and scissors, magazines for collage....
Creations: We have a box that is designated the "creation box" it is filled with all of those great little trinkets that you know could be used "someday" like yogurt cups, and baby food jars, cardboard tubes, string.... the rest is up to your recycle bin and you!
Last but not least, if you can, let them run around outside! Sometimes if the boys are working hard I will let them trade off, one subject with me, then go outside and trade with their brother. They love all the great breaks they have outside, But that is only of they work hard (is that a bribe?