If your friends are in Australia or need Australian dollars as travel funds, it is acceptable for you to give them Australian dollars in cash. However, if your friends don't need Australian dollars or are not in Australia, they may encounter some difficulties because Australian dollar cash may not be accepted by local banks or currency exchange agencies.

Therefore, before giving Australian dollars in cash, it is best to confirm whether your friends need Australian dollars, or whether they can easily change Australian dollars into the currency they need. If you are not sure, you can consult your local bank or currency exchange agency for more information and suggestions.