I get the same little "sac" of goo left in my shells when a chick hatch's.
I have always assumed it is waste product [excrement] from the developing chick during the 21 days.
Chicks are always strong and healthy though when I have only had this left in the shell after hatching.
I don't think you need to offer it anything till it is a day or two old...
I haven't ever seen that before but then again I have never incubated eggs.
How is he doing??