In Thailand, there are a few things you should do.
1. Eat until you explode.

Even street vendor foods in Bangkok are perfectly safe to eat. Culturally the Thai are VERY proud of their cooking and would be horrified if anyone became ill from their food. If it looks delicious in Thailand, eat it. If it doesn't look or smell so delicious, try it anyway.
2. Thai knock-off tailors are the best in the world. Ask your hotel concierge which tailors they recommend. You or your girlfriend can have high end designer clothing made in a day and no one will be able to tell the difference (I have a bunch of Versace Thai-made cocktail dresses). A dress or suit that would normally 15K will cost you under a $100usd in Thailand, and it will be custom fit to you specifically.
While in Fiji, there are a couple of things to do.
1. Take a boat trip to some of the outer islands. The crews are a blast and their goal is to make sure you have a really fun day, and you get to see a lot of really beautiful scenery.
2. (this one I really recommend) if you can stand hiking 3-4 miles inland on easy to moderate terrain, go with a guide out to visit one of the native villages. It's an experience you'll never forget. (take a gift for the village chief... I recommend some tea and good tea towels of all things!)
My ONE warning abou Fiji is that you should hang on tight to your belongings. Pickpocketing and purse snatching is a real issue in Suva and other larger tourist towns. Just be aware that for all it's tropical beauty, there is a darker side. Be on alert for your personal safety in the larger Fijian towns, especially after dark.
Las Vegas
1. Unique exciting city. However, you might want to consider how much time you're going to spend in Las Vegas on the Strip. Most people are fairly overloaded, exhausted and irritable after being there for more than 3 days. Take good walking shoes for this city, you'll do more walking there than anywhere in your entire life.
2. Go see a few shows. I've seen tons of them, my favorites are still Blue Man Group and Cirque de Sole Mystere. I saw O this spring, I recommend Mystere over O. Vegas is about the best city in the world to just park yourself somewhere and people watch. LOL.
California
I don't have much to say about LA and San Francisco, other than San Fran is a beautiful city, take all the tours you can find, definately visit the Fishermans Warf and Chinatown. LA? I don't have anything good to say about it. I'm sure other people will tell you different.
Hope that helps a little. I'd love to give you tips on Oz, but I've only been there twice, and each time it was for less than 8 hours. haha.