Aloha - congratulations on pondering this brave new world! Personally at 20 I would have been scared to go alone but, knowing what I know now about HI - I would do it!
look at want ads in the local papers online, healthcare is a pretty big industry especially on Oahu - it is likely you could get a job, but be sure to do your research.
Cost of living is higher in HI as most things are shipped in, so, if you want to do this, you may be doing with less - but really how important is the DVD collection or your going out for dinner habit when you're living in paradise?
If you cant get a friend to go with you, make sure you find a good group of people to meet once you arrive. Join groups that have similar interests, if thats church, volunteering, surfing - get involved and build a base of great people around you, that will help a lot!
I've included links to local papers, grocery stores and a few apartment finding sites - also if you come to www.hawaii.com and join the message boards, there is a board dedicated solely to people hoping to relocate to HI (I'm msutton8)
Best wishes on your adventure!