Practically everything. "Exotic" usually just means not native to the area.

Apples, plums, peaches, things like that.

Some islanders are fascinated by succulents and cacti.

Tulips won't grow here. Peony, many of the iris, most of the stone fruits unless you're very specific about the cultivar. There's still a lot of "exotics" that are exotic even to us, though. Most of the custard apples are still in the "exotic" category, a lot of the tropical fruits are, too.

Most plants are/were imported to Hawaii, so a lot of the semi-tropical and tropical ones brought in are still exotic to Hawaii.