Just like an emergency fund is good for covering unexpected emergencies, an opportunity fund is good for unexpected opportunities.
Even though I haven't filled my opportunity fund, I took a chunk out of my checking account recently because I saw an opportunity.
I just came back from Austin, Texas where I spent a week for vacation. The previous time I went down, I brought my camera (a Canon DSLR), three lenses, an extra battery and the battery charger and packed it in my carry-on with my laptop. I ended up taking 0 photos. The most recent trip down, I decided not to bring my camera, and when I got there, my friend was looking forward to taking photos with me at Zilker park.
I had a choice. Either forget shooting at Zilker, or go buy a camera.
I've been wanting to purchase a point-and-shoot camera for about two years now, and none of the cameras that I had looked at were meeting my criteria. Getting my "real" camera around and carrying it when there's a large possibility that I'll not use it is a pain. I wanted a second "daily" camera I could have with me at all times.
What I was looking for in a camera:
8x Optical zoom +
Canon or Nikon
Small enough to fit in my purse
Less than $300
I went to Best Buy to look around. I found the Canon SX120IS. It had 10MP, 10x Optical zoom, was small enough to fit in my purse, and it cost $250. Since it fit my criteria, I happily purchased it, finding that it also has the same features as my DSLR (aperture priority, shutter priority, manual, etc) as well as manual focus. I'm continually finding that I'm very happy I made the choice to purchase this camera.
Here are photos from my trip.
If I didn't have the extra room in my checking account (which would have been placed in my opportunity fund) I would have been camera-less in Austin, missing the opportunity to shoot in Zilker and the house in which I stayed.
Opportunity funds are great for things you would like to purchase that aren't in your usual expenses and aren't emergencies. I'm guilt-free and I don't have to dip into savings to purchase the camera. Good place to be!