Frag #11 -- Other: This may be an afterthought, but it is more likely that the student was stumped by how to handle the sentence structure. The preceding sentence ends with a prepositional phrase that lists meal times. The writer may have wanted to add "in swimming," but sensed a difference in type of category. The probable repetition of "and" may have thrown him: "But we got to be together in Breakfast, lunch and dinner, and also in swimming and [sic] all groups get together." This explanation gains further support from the "and" which appears where there should have been a "when." The "and" problem, in other words, may have been floating around in the writer's STM.
Frag #12 -- Subordination:  ". . . and everyone had to take music class, because no one wanted to take it." Personally, I prefer this as a fragment. Its being cut off from the main clause not only emphasizes the difference between "everyone" and "no one," but it also emphasizes the logic of the "because" clause. Do I perceive some subtle questioning of the camp leaders' reasoning here?
Frag #13 -- Acceptable:  Although it could be joined to the preceding clause with a comma or a dash, I don't see any problem with this as a fragment. I doubt that anyone would have any problem understanding it.
Frag #14 --  Subordination:  "My room was not neat, because hardly anyone usually got up that early in the morning." Although I have put this in the subordination group, I have no trouble with it as a fragment. To me, the full stop of the period and the fragment fit with the conversational tone of the writing and also suggest a slight reluctance to admit that they all preferred sleeping to getting up early to clean the room.
Frag #15 -- Afterthought: My guess is that the writer had the "excuses" in the preceding clause all in STM at once: "And then you had to take a shower and get dressed and then wash your face and brush
your tooth." [I hope someone pointed out to the student the humor implicit in "tooth."] Having written these down, and closed with a period, the student may have felt that, as excuses, they were not sufficient, but he could not think of any more. To suggest, however, that more exist, he added the fragment.