Just got back from a retreat. What Itake depends on how the retreat is set up. At this one, I did not have a lot of room around me but had a large place to lay out (temporary) or cut out. The cutting table was a little tall for me so I was glad I did not have to cut out a lot.
So I took some paper pieced projects that were semi prepared, and simple blocks I could lay out one at a time at my machine and sew. I could have laid out a bunch of blocks but would have had to take them up and number them so others can lay out or use the table.
Irons are usually at a premium. Dont plan on ironing all your fabric or the whole quilt or anything that requires a lot of time spent at the iron at one time. It is also good to get up from the machine and walk over to the iron for some exercise. NOTE: very few places have the electric needs to run irons at individual stations. Dont bother bringing an iron of any size unless asked.
At our shorter guild retreats, we have a lot of space around our machines and huge floor space but a small amount of cutting out space and few irons. I also want to spend less time setting up because time is short. So there, I take very simple projects set up in bags ready to sew.