Great list and I'd like to add the following:
Pin cushion
sleeping bag/bed linen - we have cots w/mattresses but need your own bedding
Credit card/money to shop 5 local quilt stores
CD player w/sing & dancing music (our group loves Mama Mia, old Beatles, many ballads, etc & use rotary cutters for mikes)
starch & sizing
camera (to photograph projects)
munchies - nuts, chips, crackers, trail mix, fruit, etc...
Chocolate to share with all
And one other thing
1 yard of Basic Brown cotton fabric - it's a running joke in our retreats but it always saves someone's project.