Geneva, You posed a great question! When I go to a retreat, I try to pack projects that don't require "thinking or cutting" because I get too distracted with all the cool ideas that I am seeing and of course trying too! Also, I generally make a mistake so I cut before I leave home!! I bring a handwork project--once, we were without power for about half a day. I was thankful that I had brought an applique project. I snuggled up in bed with my "Beam and Read" light and appliqued away.
I bring a plan of what to do with the retreat squares. I bring a top to pin as I can use the tables either early in the morning or late at night and have a project ready to quilt. I have spent the entire retreat quilting a project. Now, my quilting machine is too heavy to transport so I don't bring projects that I can't sew on my featherweight. I often bring blocks to set in a top as there are people who will offer their thoughts on a setting. I bring simple piecing projects and I piece several blocks at home so that I know it is all going to work!!
I usually have a project that I'm working on that uses scraps so I bring that. Sometimes, I bring projects that I'm sewing for the granddaughters. I try to think about what I want to accomplish at retreat a couple months in advance and then I prepare a little each week so that when it is time to pack, my projects are at the ready.
I like most types of quilting. This means I will start a variety of projects just to try something whether it is a technique, a pattern, a batting, a thread. . .well, you get the picture. The variety is what keeps the projects interesting!!!