I like to have a large square of batting, a flannel backed table cloth to layout a quilt or other project.
I also bring a couple of zip lock bags, for scraps or cut up pieces.
I actually prefer to pre cut my projects ahead, and sew them together while on retreat.
within a couple of days before going, I clean and oil my machine, and prewind 4 to 6 bobbins.
I will add anything else if I think of it