These people might all have had colds, or be allergic to your deoderant, shampoo, or cat and dog hairs.
Personally, I would not offer an adult a hankie because he or she was sniffing, but I might well ask if they are allergic to cat hairs, as I know my clothes cannot be entirely free of them, and I also know how troublesome allergies can be.
I might well give a small child a hankie, or offer one to the grown-up witht the child, though.
Basically, I think good manners requires us to ignore people sniffing, passing wind or hiccoughing in public. They are presumably not doing it for the fun of it, or annoy us.