School districts can award emergency teaching credentials if their need for substitute teachers is dire enough. It usually is dire enough.
There are many books on substitute teaching, but only a few written specifically for high-school substitutes. High school calls for a completely different approach from K-8. This book explains not only how to get a high-school substitute teaching job, but also how to do the job so well that it will be rewarding in and of itself. Being an excellent substitute can also open the door to a regular full-time teaching position.
Up until the advent of the Internet, most books for substitute teachers consisted largely of worksheets the substitute could photocopy and hand out to students. Today, you can instantly find and project one of a million free Internet worksheets. Heck, 99% of today's high school students have phones capable of finding these worksheets.
You won't find worksheets in this book. High school students are too savvy to do a substitute's ungraded busy work. Today's high school students crave human interaction. I've seen them get more excited about a classroom discussion than about watching a movie. Times have changed, and I have remained a successful high school substitute teacher by embracing the changing times.