@bertha: I probably have different hair challenges than you! My hair is roughly chin length. And I relax it to straighten. Moisture is the enemy for me! If it seems like a hot day, I typically get a wicking headband to use to deal with the back of my neck, and make sure no hair is at the edge of the helmet. When my hair is longer than the helmet, I try to loosen up the back so it doesn't press too closely to my hair.

I am making some assumptions about your hair, and assuming you have straight-ish longer hair. Think a french braid! A bun! And i have seen some awesome articles on refinery29 for helmet hair.
What To Do With Bicycling Helmet Hair
Wearing A Bike Helmet Hair Ideas

BTW: I have this basket for my rack, and it makes grocery shopping a breeze! https://www.amazon.com/Basil-Memorie.../dp/B0030SZ0HC

It fits most of my backpacks too.

If I recall, you don't have a helmet yet. I went for the "cute" helmet and grabbed the nutcase urban helmet. I live in the mild bay area, where it rarely gets 80 (used to but no longer). Now that is has been so hot, I realize there is nowhere near enough air holes! So I'd get more ventilation in a helmet, since I know Boston is pretty hot in the summer! Less air holes + more heat = helmet hair!