Cherry stones/peach pits/etc.
Seeds would be valuable, as you can plant them (savings acct), nurture them (savings with accumulating interest over time), gather your fruit (collect interest), and plant more seeds (diversifying), without losing the worth of the original seed (Profit!). Also, different kinds of seeds are worthwhile, as some make trees, which become sources of revenue if properly cared for, and you can also just trade higher commodities for young trees, offering a faster return at less development time.