[Holbytlass]

I'm not sure if the list was meant to go in order....

17-Fatty Bolger stays behind to cover Frodo's trail
I find this situation to be very interesting. At first, Fatty feels that the Old Forest is "quite as dangerous as Black Riders". He had not encountered Black Riders with Frodo, Sam and Pippin nor has he been in the Old Forest only scared by the bogey-stories told by his nurses.

He stays behind to keep up pretense that Frodo is still there and to give Gandalf the message of where the company went to, but Fatty also stays because he had no desire to leave the Shire.

On the same night as Frodo and company meet up with Strider at the Prancing Pony, Fatty meets up with some of the Black Riders. He saw them creep in the garden and he ran more than a mile to the nearest home to (finally) raise an alarm.

I personally think that even though Fatty is fond of Frodo, had he really known how dangerous and scary Black Riders were, he would not have even stayed at the Crickhollow house to keep up pretenses or to give Gandalf the message.