Are the campsites first come, first serve in October or do I need a reservation?

Go to the website and reserve your spot. You can move if you get there and want a different site. But at least you are guaranteed a spot before you get there.

All campsite in the F loop are first come first serve. Everything else requires a reservation. I recommend getting there early to look at the check out dates of the camp sites and hang out at the lake until its check out time and then snag your spot. I forget when check out time is unfortunately. If you cant find a spot you can go to Wahtum lake near by that has camping spots as well!