As a substitute teacher, it is important to show up early for every assignment. Showing up early allows you to go over the teacher's lesson plans and make sure you know where all the materials for the day are located. It also allows you to create subbing plans if the teacher did not leave behind plans or if the plans are unclear.
If you arrive in a classroom where the teacher did not leave any lesson plans, one of the first steps you should take is to visit a nearby classroom. Nearby teachers might be able to provide you with materials to keep the students occupied for the day. They may also be able to provide you with information on what material the class was covering, which can at least guide you in the right direction.
Another place to turn is the students. While you do not want to rely on the students to provide plans for the day, they can sometimes help. For example, if the teacher left plans, but some of the phrasing is unclear, the students may be able to help you understand what needs to be accomplished. In some cases, asking the students what material they covered most recently can help you understand what needs to be accomplished next.
Unfortunately, sometimes turning to nearby teachers or to the students does not work. As a substitute teacher, it is a good idea to have worksheets or other activities you can have the class do if the teacher did not leave behind lesson plans. Include worksheets or activities that appeal to a variety of ages and subjects in your sub bag. Coloring pages can keep younger children occupied for a while. Trivia games (whether subject-specific or broader) can keep older students occupied. You could even have older students create their own trivia questions based upon things they have learned recently.
There are many websites that can give you potential emergency lesson plans based upon specific subjects. It is a good idea to make sure you have age-appropriate teaching activities available before you leave for any substituting assignment. Even if the teacher leaves plans, you may need to use these activities as fillers if the teacher's plans do not fill the day.
One important thing to remember to do is to leave the teacher a note at the end of the day, explaining what you accomplished. Yes, this is important to do even if the teacher did not leave you lesson plans. If you have encountered a situation where the teacher either did not leave plans or left inefficient lesson plans, what did you do to make the day productive?