Go buy dollar store umbrellas and hand them out polling places.
Several cycles ago it was raining and I saw people standing in line waiting to vote in the rain in the morning, so I stopped at the Dollar Store and bought 20 really cheap $1 umbrellas and handed them out at a couple polling places in my city. I told people to continue to pass them onto other when they got inside. No one told me I couldn't do that.
I was really proud of myself when I came home from work in the evening and saw people in line still using the umbrellas I handed out.
Edited: People said it is legal so I am amending this thread to be a suggestion.
= new reply since forum marked as read
Should be good to go as long as there were no political stickers on em. 
I in the south somewhere in past elections, I saw people who bought or brought lawn chairs to for people to sit in. It's just a humanitarian gesture so there shouldn't be a problem with that. I can't imagine anyone standing in the rain would co,plain that someone was kind enough to think of their welfare while waiting to perform a civic duty.
Other than that, 
... umbrella!” 
A great idea, kind gesture and Not illegal (at least not in Alabama). Good for you.
The gray sky changed to blue. I took it as an omen.
