I am doing a retreat next month. You might consider a mat for your sewing machine to sit on. Some tables are thin and you may get vibrations. I want to make one that hangs over the front of the table that has some pockets. You could just get a placemat made of the cushiony nonslip material or shelf liner.
Also take some extra materials unless there is a shop nearby then take some fun money. Some fat quarters maybe nice that you can swap with others if they have something you need.
Also, extension cord and a small light if you have them are nice. Do you need a design wall, you can bring a piece of flannel/sheet with some of the wonder hooks that you can put up on the wall if there is space.
Mostly enjoy!