When I first learned in 4-H, I think one of our first projects was hemming towels. Linen toweling isn't too expensive and everybody can always use new ones. We worked all the way up to making drawstring aprons (no gathering, just a placket through which a self-fabric drawstring was pulled.)
In this more liberated age, I think they make tote bags so they have something they can use, while still only doing straight stitching. Lots of embellishing opportunities, too, to personalize them.
Simple projects like totes can be used to teach adults to sew and create saleable items for your fundraiser.
If I lived near you, I would volunteer to help. I really want to teach adults to sew, but have not yet found an outlet for this desire. Tried offering on Craigslist, but no one answered.
Good luck!