Once I was in a grade 7 class and the teacher had been reading them "The Book of Awesome". The thing about "The Book of Awesome" is that each story is no more than a 3 pages long, the majority of them are appropriate for all ages, and it's an easy read.
Sadly, I missed the boat on "The Book of Awesome" and never got around to buying it at my local Superstore for 40% off (hey, I'm a cheap substitute I'm not paying full price!) but you better believe I scooped up "The Book of Even More Awesome" for the ultra low price of about $11. Once you read it (which you will because let's face it - it's awesome) bring it along with you when you sub in grade 5 or higher (if you are subbing in a grade lower than grade 5 stay tuned). If there is ever a lull in the day read them a story (or 4) from the book. Discuss what they find awesome about their day to day lives. You can likely fill an entire class this way. If you are really strapped for something to do get them to write an "Awesome Story").