a) when the L family reported BL missing and were worried he might harm himself they would have been asked to provide scent items.
It makes zero sense that the FBI would return for more scent items, after several weeks. Anything they collected should ostensibly have a weaker scent value than those items his very worried parents provided LE with when searching first began, wouldn't they?
b) I agree with others who saw what appeared to be field testing kits.
c) I too witnessed the one female FBI agent who was gloved after coming from the camper to the house, made a point not to touch anything with her gloved hands and another agent opened the door and held it for her as she held her hands in such a way that it seemed clear she was avoiding handling anything, much like a surgeon after they've scrubbed in.