Whatever you can do with a traditional currency can be done with Bitcoin. We are now at the point that there are several companies which offer to purchase an item on any website and you pay via Bitcoin.
It's not currently the most easily accessible, but we are certainly making progress.
Bitcoin as an alternative currency can be use in almost the same way as money can do. We can trade, pay bills, purchase and invest using bitcoin. Its limitation is not constant since the use of bitcoin and other alternative currencies are being studied to its maximum usage and market limitation in the future.