I'm an officer at my schools GSA club and I wanted some fun or serious topics I could use? It will be greatly appreciated!
As long as it doesn't become social hour, anything will work. I tried to go to my school's similar group, and it was a complete turnoff. It was one giant clique. Since it's a school GSA, try and keep things exciting for both parties. You could get people to do presentations on things that matter to them (I know a FtM did a whole meeting/discussion on her life) and I think it was actually a brilliant idea.
Declare a "wear jeans if you're gay day" see how many straights panic for fear of being considered gay (they do it on college campuses-with some success).
I don't have any brilliant ideas, so I'll just tell you what the GSA at my school does. The standard meeting will start out with little ice breaker questions. (Example: Who would be your dream date? What is your spirit animal?) Then someone may share their coming out story, if they are so inclined. Then they usually have some sort of themed discussion. For example, last week they talked about faith and sexuality.