Serious Eats - seriouseats.com

I think the next question will be in what recipes?

There is a great website called The Cook's Thesarus that describes ingredients and offers suggestions for substitutes. It often has pictures to aid in identifying ingredients. See here.

For your two queries it suggests:

Zucchini Substitutes: cocozelle OR yellow squash OR pattypan squash (especially for stuffing) OR chayote squash (not raw; takes longer to cook; excellent for stuffing; peel first) OR eggplant OR cucuzza OR carrots OR pumpkin (This is a great substitute for grated zucchini in breads and cakes)"

and

Blueberry Substitutes: huckleberry (larger seeds and tarter, otherwise very close substitute) OR juneberry OR red currant OR raisins (in baked goods) OR dates (in baked goods) OR bananas (in baked goods)

I confess, I don't get suggestion to substitute banana for blueberries in baked goods ...

Gingercookie, I can imagine no reason that yellow squash wouldn't work in breads, it has the same texture and very similar taste.

I see bananas working as a substitute where the good is something like pancakes or muffins, where virtually any kind of cut up fruit might work. But if you were making a pie, for example, different story.

@chgoeditor -- awesome.