Once you learn the folding method and to always use a square piece of fabric, achieving beautiful furoshiki gift wrap becomes second nature.
Using fabric that you already own is the most sustainable option for furoshiki gift wrap. If the fabric isn't already square, you can fold it to be. Scarves & tablecloths are good options!
When you thrift for fabric, you can get creative! Scarves and tablecloths are still my favorite options. You can also find actuals swatches of unused fabric, napkins (you can sew them together to make them larger), and more!
There are some companies that sell furoshiki wraps, or fabric that can be used for it! Wrappr is one such brand, and they offer beautifully designed fabric squares that make beautiful gift wrap.