I have my own little ironing board that I made from a flat wooden tv tray with several layers of felt and then a muslin cover that I like to take with me along with a small iron.
Last retreat I found silicone iron rests at Hancocks clearanced out for 25 cents each. I bought all they had, used fat quarters from my stash to make bags and took little "Hi, glad we're getting together" gifts for everyone. Not necessary but fun and cheap. One lady brought a pan of brownies to share, another a big bucket of fresh peaches from her own tree.
Make sure you take a pen and a notebook. At our retreats if someone is using a technique that someone else doesn't know we teach each other how to do it. Being able to take notes helps.
Other than that you might take a book to read to unwind right before going to sleep.