Not sure which island you're going to, but I went to Oahu last winter and had a great time. If you're normally good at finding drugs, I'm sure you'll be alright, but it took us a few days to find weed. My homie went on a Tinder date with a hippie chick just to secure it. Unless your girlfriend's really cool, I doubt that's in the cards for you. Aala Skatepark in Chinatown is basically Honolulu's version of LES, so you might have some luck there. Just be careful if you're a Haole (white dude) because the native Hawaiians aren't always so friendly to colonizers.
Other than that, we went on three hikes (1000 Steps, the pillbox one from the last season of KOTR, and the one with the waterfall/cliffjump that everyone goes to) and surfed a few spots on the south shore. The north shore is pretty scenic and certainly worth a day trip. If you're into traditional tattoos, check out Old Ironside or Queen Street Tattoo. The former was owned by Sailor Jerry and has murals of him and Mike Malone out front, the latter is just a really good shop and I can vouch for the quality of their work.
I enjoyed the food out there immensely. There's lots of good poke, the shrimp trucks are great, and I found out that spam goes really well on a breakfast sandwich.