Gil is named so because of my pure undying love for German male names (MC of our previous story was Eric). Between ourselves we joke that his full name is Gillian.
Summer was named by my writer, as I remember correctly I proposed to call her Linda, but he said something like "do you really think it's an appropriate name for a 10 y.o. MC in a summer camp"...and after that he called another character (a ginger half-Japanese goth girl) Peggy and I am still laughing at it.
We actually had problems with naming two other girls, so we randomly chosen two names that from the first glance didn't suit neither of them. In the end we decided that Zoe suits the tall pouty blonde much better and Peggy sounds better for a redhead.
Billy was given the almost the most average name possible for a teen who looks like a typical young jock. But we also wanted it to be a "younger" and more endearing sounding name, so he wouldn't be like Jack or Chase or something.
Eugene is named for the same friend I took character's likeness from. It was a very popular name in the time I grew up (it also happens to be my name), so I always thought it very average and believed it suited his calm character with a bit of cheekiness.
Jaeger was called that somewhere between us thinking that at least someone needs an unusual name and talking about Jaegermeister. Now that we have to choose their family names, we spent some time thinking if we should call him Jaeger Hunter or Jaeger Gatherer. Surprisingly or not, we stepped away from that xD