I so miss tanglewood, use to go all the time when I lived up there.
Some good hints here
http://gonewengland.about.com/librar...woodpicnic.htm
And remember to plan for any weather. Just because they don't predict rain for example in Boston, that doesn't mean you may not get some out there, even if it's a toss away pancho, it's better then nothing.
You can also rent chairs this year if you don't have any, don't plan on buying them just for the show. $4 each.