i would say that don't buy anything special for the retreat that you wouldn't use at home. it is just a waste of money. go to this retreat, then you can find out what you can't live without for either the next retreat or at home.
i went on a retreat, and some people make "kits" for themselves ahead of time, thus the major cutting would be done. i wish i would have done this, because i spent alot of my time cutting rather than showing and telling about my FINISHED quilt tops. another thing...so many people laughed at all the stuffs we brought with us. i brought practically my entire collection of black and whites when i probably should have cut ahead of time. it would certainly have saved time at the retreat.
also, 30 minutes away is a quilt store? 30 MINUTES??? what were they thinking? anyway, 30 minutes is close enough for a small excursion. i am sure someone would want to go. i always visit quilt stores if i am that close!
above all, have a great time.