Sarah,
Welcome to Travelblog! Congratulations on having the courage to follow your dream. I was really nervous the first time I did it too; the excitement quickly made the nerves disappear.
First, for logistics Travelblog has an entire guide on the subject: http://www.travelblog.org/Travel-Guide/ It covers what to pack, what needs to be planned ahead of time, how to find places to go, and similiar topics.
Being on the road alone, you meet people along the way. Hostel stays are great for this, along with couch surfing. For the latter, it helps to host people first so you build a reputation online before you need to find a spot.
I can't comment on Australia (except for the blogs I've read) but many Travelblog members are based there and will likely have advice. For the US, here's the basics:
1. You will need to apply for visa approval in advance to stay longer than three months. It takes at least a month to get.
2. US working visas require a sponsor who agrees to hire you, almost certainly at a summer camp. If you like that type of work, it can be a great way to meet people. These visas can be hard to get.
3. If going alone, the minimum cost per day is $60 US. This assumes staying in hostels and campgrounds, using buses for travel, eating fast food and other street food exclusively, very little paid attractions, and no souvineers. It could easily be double that.
4. US Customs tends to be harsh on people who can't demonstate they have enough cash to cover their entire trip. The political climite is very chilly about non-citizens working in the country currently, and the customs routine reflects this. Expect to show a credit card or two, plus a bank account with a descent amount of cash in it. Don't let this scare you, though, nearly all travelers get through with no problems.
5. Rural areas in the US are hard to reach without a private vehicle. Minimum rental cost is around $25/day, plus at least a $20 premium if under 25. Buses and trains go to many smaller towns and some National Parks, but can be very inconvenient. Bloggers have certainly used them. The alternative is to sign up for one of the group camping tours run by companies like Trek America (the blogs I've seen than mention these trips rave about them) but they aren't to everyone's taste. Many involve lots of alcohol consumption, for example.
6. Traveling without a plan is easy in the rural parts of the US, and often incredibly fun. Except near national parks, during holidays, and for festivals; lodging rarely sells out. National Park lodging, on the other hand, should be booked six to nine months in advance. If that's too much, its easy to stay in nearby areas and travel in for the day.
7. US wilderness areas are incredibly beautiful, and have enough adventure opportunities to last for years. Many US based travelers never leave the country for exactly that reason.
Good Luck. Your trip will be a life-alterning adventure! Please remember to blog it.
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