Was going to mention that the Frolic UFO came to me in a large flat rate post office box and that has been a very nice generous size yet easy to carry around and is about the size of the box I've started for Grassy Creek. I'd also recommend a trip to the dollar store and get some Gallon sized bags or what ever they have for largest size as well as a box of more sandwich sized bags. I ended up buying a bunch of large clips there last year that are heavy but super easy for large groups of fabric/blocks, and can also grip single layers as well. I also now have a lot of those nice little quilter type clips for the subunits.
When the UFO came to me, it had all the front loading stuff done and units were clipped into sets and those put into large nice ziploc baggies with the clues marked on the bags. I went through the different bags and units and put together all the parts needed for each block into a cheap quart baggy of its own. I had a sharpie that wrote on the bags and I numbered them just because bags are slippery and sometimes I'm clumsy and sometimes I simply loose count... If your markers don't work on your bags, perfect time for some blue or masking tape (both available at the dollar store...) to make a label and write on that.
edit: I found I had two tubs in my sewing room, think large shoebox sized that were a perfect fit across for the bags of block pieces! Not sure if they were from the dollar store or not, but got those slippery bags handled at the end. My Tuesday group ladies tease me sometimes with my project boxes and bags such, but deep down I know they are impressed on how I can always have a project to work on at group
