North Topsail Beach, Onslow County: NTB Police can be heard on the VHF sheriffs dispatch channel as well as the Onslow/Jacksonville trunked radio system.
Fire in Onslow County is mostly on VHF, but some 800 crosspatching, the same with Onslow EMS. They have a conventional 800 P25 system, use the County trunked system some and that is crosspatched into the VHF EMS frequency, 155.400
On the Pender County side of things, Pender uses the NC VIPER system almost exclusively, but they still have VHF crosspatched to VIPER for fire and EMS paging. The Holly Ridge site on VIPER is very close to the island and you will catch better than 90 percent of Pender County's 800 traffic on that site, plus lots of other users as they pass through.
As far as Amateur Radio, Wilmington has a number of 2m and 70cm repeaters. You also have Jacksonville has two 2m repeaters, but getting into those on a handheld from the island is most likely not going to happen. One repeater is in Hubert at 286 feet and the other is on top of Onslow Memorial Hospital.
There is also a 70cm repeater in Hubert, 444.675 + 88.5 ENC/DEC that has handheld coverage on the island in a number of places as well as Snead's Ferry.