So far the best reason they’ve given for everyone to go is “We’re supporting Emma,” save for Gold, who is there because blackmail (and also his blood yadda yadda).
It would have been different had this plotline been done to save Neal at the end of S3 as I had hoped back then. Regina would have come to support Henry, and Henry & Rumple would have come for their own connections to Neal. Robin and the Charmings STILL have kids they should be caring for and almost zero cause to seek either of Emma’s loves (except to support Emma/Regina), but whatever. Actually, after Emma, Belle has the best relationship with Hook at this point out of the whole group and she got left behind (and she also had a good relationship with Neal going, so…). So whatever. Some logic got thrown under the bus to make this plot work.
Keeper of Belle's Gold magic, sand dollar, cloaks, purple FTL outfit, spell scroll, library key, copy of Romeo and Juliet, and cry-muffling pillow, Rumple's doll, overcoat, and strength, and The Timeline. My spreadsheet: https://drive.google.com/file/d/0B6r8CySCCWd9R0RUNm4xR3RhMEU/view?usp=sharing