As you can see, the State of Hawaii land masses are located in eight grid squares: BK28,BK29, BK19, BL20, BL10, BL11, BL01 and BL02.
Hawaii
Maui
Kahoolawe
Lanui
Molokai
Oahu
Kauai
The Big Island has Four Grids
The Big Island, including Hilo, is mostly grid square BK29. The BK29 grid takes in about 80% of the island. It has a southern point, called strangely enough "South Point", that extends below 19 degrees North Latitude and falls in BK28.  It has a western section that crosses 156 West Longitude at the Keahole Kona Airport area and falls in grid BK19.  It has a northern tip which crosses 20 degrees North Latitude and falls in grid BL20.

This makes the Big Island the king of the islands in terms of grid locators, with four major grids on its land mass. True there is an eastern tip that extends across the 155 West Longitude line, but remember that grids are two degrees wide, so this is still grid BK29.  Close to the south edge of the Big Island, but well offshore is the grid BK18, but it misses landfall.

Molokai is all BL11 Along with Eastern Oahu
All of Molokai is in grid BL11 which it shares with the entire Eastern half of Oahu. Honolulu, Kailua, Kaneohe, Hawaii Kai, all areas like this are in BL11.

Western Oahu and Southern Kauai are grid BL01
The Western half of Oahu, starting about at Waikele Shopping Center, is in grid BL01. Pearl City High School is still in BL11, so people near that area would need to check a map looking to see which side of 158 West Longitude they really are on. Oahu shares BL01 with the southern half of the Island of Kauai. The northern half of Kauai is grid square BL02.

Maui Touches Three Grids
Maui is mostly in grid BL10. However, there is a very tiny part of the far Eastern tip of Maui the slips over the line and into grid BL20 which is shares with a rather large chunk of the far north end of the Big Island. On Maui's far Northwest tip, a thin strip is north, across the east/west line of 21 North Latitude and into the very popular grid BL11.

BL11 Scores as the Most Populous grid in Hawaii
So, BL11 which includes a tiny bit of Northwestern Maui, all of Molokai, and the eastern half of Oahu is the most populous grid in Hawaii. However, BK29 may score highest in terms of most land area (non-ocean area) in a Hawaii grid.

----------------------------------------------------------------------------------------------------------------

One of the possible VHF/UHF awards in Hawaii is the VUCC award. At the higher frequencies only five grids are required. There are places on the Big Island where five grids can be contacted from a single site.