Hartinger, Brent. Geography Club, The Order of the Poison Oak, Attack of the Soul-Sucking Brain Zombies, and The Elephant of Surprise. Buddha Kitty Books.
I first read Hartinger's Geography Club a few years ago, when I was catching up on my LGBT books for teens. The story focuses on Russell, Min, and Gunner, who attend the same high school and end up starting a GSA (Gay-Straight Alliance) at their school.
The next books in the series follow the same characters - Poison Oak deals with summer camp, Brain Zombies has to do with a movie being filmed in their town, and Elephant tackles the topic of freeganism. The books are harmless fun, predictable, and have a few small plot twists that may surprise younger readers. I enjoyed each one as a quick fix of "brain candy" for an hour or so.
However, I have realized (having read the second and third books in one day and the fourth book the following day) that these books are following the standard of the Babysitters Club books from decades ago: tell the same basic story, with the same characters, changing just enough so that people continue to read. If you like series fiction like that, these books are perfect for you. However, if you want to read things that are completely different from each other, pick one of these books and skip the other three. If I had to pick just one, I'd probably read Poison Oak. It's my favorite.
And no, I don't know what a brain zombie is.