No worries, mate!
I've been diligently learning my kiwi slang this past year, all the "yonks" and "dags" and "hoons." It's best not to have a vacant expression when someone says something unknown to you. But the one saying that I've taken to with reckless abandon is "No worries, mate." I believe it deserves worldwide importation. It's such a marvelous one-size-fits-all saying, one I find shooting out of my mouth at every opportunity at work lately. Page layout changed with 10 minutes to deadline? "No worries, mate." Accidentally put the picture of Gandhi in the story about the serial killer from Liverpool? "No worries, mate." Coffee machine on fire? "No worries, mate." Actually, I really need to say it a bit less often.
What's marvelous about the saying is that it can take on whatever tone you want. It can signal can-do optimism, resigned bravado, or just take the place of "uh, dude" in California-speak. It's actually a little bit emblematic of the Down Under spirit, where whining is far less accepted than it is in the US, where few tasks are seen as impossible. I wouldn't call it "resignation" really but "no worries mate" implies that we'll do it, we'll have a bit of a laugh and won't whinge (kiwi for whine) too much in the process. Not a bad philosophy, really. "She'll be right!"
(Once again I refer to to the fine Kiwi Slang guide so you too can speak like a kiwi.)