The larger the bill, the more valuable. They're pretty colors too. Credit Cards Don't bother with traveler's checks. ATM machines are omnipresent, even in smaller towns. On the rare occasion that a machine didn't like my card, I could find another machine within a block that did.
Credit cards are surprisingly hard to use.
The fees that banks charge merchants are exorbitant, and so stores tend to discourage their use. Minimum purchase, and so forth. Many smaller places and hostels don't take them at all. Plan on carrying more cash than you're used to. The pay phones in Australia do not accept incoming calls.