I always take two machines to a retreat or workshop. One stays in the car unless someone needs it. It's not that uncommon for someone to forget a foot petal or plug and be stuck with no working machine. One retreat member had her machine mess up, every one there but her brought an extra machine. She had her choice of a lot of featherweights!
I keep a small first aid kit in my sewing tote for retreats. Bandaids, Neosporin with Pain Relief, Aleve, Benadryl, and Excedrin.