Great advice above. I keep a list in one of my sewing bags, so I know what I want to take each time. I take a long corded surge protector for my machine as I want it protected.

As for irons: some retreats supply the irons and request you not bring any with you to prevent power outages. Irons take up a lot of power. Also, this way they can be confined to 1 or 2 areas so that is a safety issue. No chance of being accidentlly burned by your quilting neighbor's iron.

I also take at least 1 plastic cup with a closing type lid for my coffee/water/tea. I surely wouldn't appreciate it if someone's coffee spilled onto my work, so I honor others this way. I also honor my own work this way.

I am going to one this week end, but this is technically a day camp! Thirty of us going, we all have a part of one meal we are responsible for ( doing Thurs nite dinner with 3 others). We go home at night, might be 8:00, might stay until midnight! I love it!! Also like the away retreats, doing an embroidery retreat in March that is very very nice in a great convention center/hotel.
I bring my own coffee mug or travel cup, hate styrofoam cups. I also bring my rolling chair, small table and ironing pad.
I enjoy this day camp, too!!

Chocolate and plenty of it. Enjoy your retreat. I go on an annual one - with all of the suggested items and chocolate - and they are great fun.