I have since hit on the idea of organizing my tools and materials into 3 phases when taking things out of the studio, and only taking through the phase I think I will need. Keeping items organized like this also means you can leave them in the car at a retreat or sewcial and only bring in each phase if you get to it, cutting down on hauling, and preventing things from straying/exploding all over. For each phase I like a big plastic tote or blue Ikea bag that smaller totes can fit into(see Flaun's excellent post on snapware).
Phase One: Cutting and Piecing
You could even divide this into two sections. I generally do all of my main cutting at home as I tend towards the scrappier style of work but it is important to bring cutting tools for trimming and squaring up. Also bring some alternate fabrics in case you aren't sure about part of your design and extras of the main fabrics in case there is a disaster.
Here is a good checklist to give an idea of things to bring for a retreat. Basically all of the things you would need for cutting and piecing your top like thread, snips, sewing needles or machine, cut pieces, iron and board, cuttng tools, pattern or book, seam ripper, etc. would comprise the Phase One bin.
Phase Two: Backing and Basting
If you get the quilt top done, congratulate yourself and go dig out the Phase Two bin. In here are the materials for backings, batting, curved pins or adhesive spray, blue tape, gadgets for closing pins, and shears for cutting batt. At home I also keep a ginormous drywall square ruler in with these things to measure and square up battings and backings. ( I don't normally haul it on the road with me, but I would if I owned a van...)
Phase Three: Quilting and Binding
This is the smallest bin, unless you are hand quilting and have a big hoop. In this one goes special feet for your sewing machine(if they don't fit in the machine's compartment), quilting gripper gloves, Teflon sheet for machine bed, marking pens or tape, quilting thread and needles, binding strips and binding ruler, lint brush, and a hand sewing kit. If you are hand quilting, add a hoop or two, some thimbles, and a pliers.
I'm sure I am missing things (I usually am...) on these lists as they are not meant to be exhaustive, but only to give an idea for organization. Another idea I like a lot is bringing a checklist with you so when you are packing up you can make sure you round up everything you brought.
I almost forgot the most important tool---your creative imagination! Don't leave home without it!