It's great to hear your enthusiasm around teaching! I second skidude's suggestion to take a level 1 course. You'll learn more than you ever imagined, and it'll definitely improve your own skiing.
More important than having a list of activities is being able to assess a learner for their skiing strengths and opportunities, then creating a development strategy to help them improve the skill. After assessing the skiers, a good instructor chooses one tactic and tailors it to the different needs of everyone in the group. For example, you may have a group like this:
Skier 1 rotates his upper body to create turns
Skier 2 is skiing in a wedge despite displaying no skill deficit
Skier 3 is leaning over the inside ski throughout most turns
Skier 4 is skiing z-turns
Which exercise would you use with all of them? How would you customize it to create improvements for all the skiers?
So why this whole cautionary tale? It's so easy for new instructors with good intentions to throw out drills without understanding what they're trying to develop in skiers. A classroom analogy would be drilling students on quadratic equations when they actually show a deficiency in their multiplication tables. (unfortunately our school system is structured this way in North America, but that's a whole other discussion!) While I'm not saying this is the case for you, I just want to set out that expectation that it's more important to understand skiing skills and be able to assess, rather than knowing a long list of exercises.
That said, skinerd has made a list of exercises (which he's presumably used with his Section 8 training program). You really don't need to know more than a handful as a new volunteer. I know a quarter of that list, and am not lacking for exercises. As long as you have a few exercises in your pocket and good assessment skills, you can customize the exercises you do know to target the skier's needs.
Keep in mind that exercises are a small part of ski teaching, and represent only one of many tactics to create a change in a skier. A couple of other easy tactics include getting your group to just follow you, or giving a visualization/kinaesthetic cue and a specific goal ("See how far you can turn uphill at the end of each turn before starting the next one.").
Good luck with teaching!