Margaret worries that her having to testify on Communist activity will embarrass her father, but she had earlier implied to Henry Blake that her father was dead.
When Margaret is talking to Williamson in her tent, Loretta Swit's fingernails can be seen to be an inch long. No nurse, especially a head nurse, would have fingernails that long.
When the Congressional aide first visits the swamp, while BJ is lying in his cot, where the tent is cut away to allow for the cameras, the sky is visible in the top right corner.
Cpl Klinger snaps a picture of Margaret's dinner and says "still life on a shingle" before the chef has plopped the gravy on the toast. Therefore, it's nothing on a shingle - it's just toast.
However, given the frequent derogatory comments on the unit's food, describing the toast as roofing material could be seen as legitimate criticism.