We've always recommended having a good emergency fund set up for when things go wrong. However, not all of life's surprises are bad. You should also consider setting up a fund for when opportunities find you.
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JD Roth at Get Rich Slowly recommends building an opportunity fund so that you can take advantage of unexpected opportunities. Obviously, this comes after you handle the basics. Pay off your debt, make sure you establish an emergency fund, and set yourself up for automatic investments into your savings and superannuation. If you have money left over, or you receive a financial windfall, consider putting some of that money into a fund that you can access quickly should a good investment opportunity arise. You never know.
The opportunity fund: How to be prepared for lucky breaks [Get Rich Slowly]