I've only been on 2 retreats. However, I brought everything I needed to finish the top and back for the (ugly) quilt I was working on, enough material for 2 other quilts & patterns I wanted to make, cutting mat, rotary cutter, pins, not enough (good quality) sewing machine needles-had to purchase more at LQS, snacks (salty, sugary, caffeinated tea, sugar-I use special sugar) and money (as we went on a couple of field trips to LQS)!
I accomplished a lot at both retreats! I had a great time at both, but learned what I do and don't like and expect out of retreats!
I hope you have a wonderful time and look forward to seeing what you accomplish at your retreat!