Ask the organizers what is included and what you need to take!
There's no sense in taking more than is necessary ... and at the same time, you want to be prepared.
I'd go with what they tell you to bring ... and have some extra things in my car "just in case".
As for what you will do ... here's how some retreats in my area do it
* you pick fabric ahead of time, and they prep it ready for you to sew Mystery Project!
* you are told yardage and type to get, for a Mystery Project
* you bring your own project
One in this area is pretty deluxe ... you stay at a B+B Spa, with next thing to five star meals. A massage included and other spa treatments available for extra $. You take your sewing machine and basic supplies. All the other things (cutting mats, rulers, rotary cutters, iron and ironing boards etc) are there for you. Makes for a lot less packing!
And then there's others ... that are pretty much like moving your whole home, including taking all the food!
So ASK!!!!!!!!