I will go with Turnips.
I remember on the gamecube on the game Animal Crossing every saturday a lady at 7 am would be on the town selling Turnips. You could get the turnips really expensive, or really cheap. Depending on the price I would buy a lot. Then everyday I would go with Mr. Tom Nook and see the deals he had for the turnips. sometimes I could triplicate my money or even more, or sometimes I would not even get my money back. I remember that game, and I would never forget all the memories I had. I remember playing it in 2005; at 4/5 years of old. Until the date I play it, but only the GameCube version.