I put my mat in the case with my machine. It stands up in the back of the case. The case is also big enough to hold my extension table if I take the legs off. I just pad it with some of the fabric I'm taking. Never had a problem with the mat warping. The rest of my stuff goes in a large tote bag, including my travel iron and folding ironing mat. Lots of times they have ironing stations and some places don't allow you to have your own iron so you might want to check on that. If you forget something, chances are you can borrow from another quilter or take a quick trip to the quilt store. Most of all, just enjoy the experience. Retreats are so much fun.