5d forget to order vermouth (4) o?i? perhaps it's omit and an order of vermouth makes one vomit
26d an island heaven, it's said (4) ???e if it's Skye the clue should have been heaven when drunk
27a their much smarter than their mates (8) p???o??? peacocks? not smarter than peahens who don't get needlessly plucked -- so pluckier would be a good clue
24d runaway debtor in a mess (5) d???n if it's drain the debtor must be Dr. Ina who patients never pay their bills