I am in zone 4 and it isn't too late here at all- I suppose it depends on your zone though... what about squash?
Iowaorganic- mama to DD (1/5/06), DS1 (4/9/07), DS2 (1/22/09), DS3 (12/10/10), DD2 (7/6/12) and a new kid due in early 2014
We ended up with some volunteer acorn squash last year, and they would've started themselves right about now - so if that's what you want I'd just plant it. Pick whatever variety with the shortest maturity, if you can be choosy. I suspect gourds would be fine too.
In order not to overwhelm ourselves with both our own and our CSA veggies - we plant celery, roma tomatoes and one other (maybe 3-4 plants total). I put in some peas this year, I like to plant leeks too.
I'd grow herbs, anything you use a whole lot of each week, anything the CSA doesn't grow that you like, and anything you want to grow lots of and preserve. In my case several tomato plants and lettuce and maybe ground cherries or melons - some kind of annual fruit.