mushrooms should be easy, i never made any but they look like they would be easy for beginners.You will need big buckets, gloves, strong spoon for mixing.

Kim, It's nice to have a handout for everyone with a list of ingredients, how to mix and equipment. Buy portland cement NOT concrete mix.
Either plastic to line your molds or a baking spray for plastic molds. Plastic bags to place your creations in (or wrap around) for curing. Wheelbarrow or mortar pan for mixing with a shovel or hoe. Have tables that are low or high enough to work on. My tables were set up too high for my first class. Extra rubber gloves because someone always forgets their's, dust mask for mixing the dry ingredients.
You can make stepping stones, mushrooms, birdbaths, candle holders, lanterns, masks, totem poles, plant stands.
What's wrong with pots/planters for beginners(or any gardener), you never have enough pots. Pots are one of the easiest beginner projects and you can make a wide variety. Have a great time. Billie

Wish I could join in the fun! Bet your group comes up with all sorts of interesting creative goodies! Have a super time!