As we all know that bitcoin now are being made as a trading pairs to different fiat money all over the world. And we you go round the world having a good vacation on different countries you do not need to bring more fiat or physical money instead bringing gadgets and connecting to internet is enough to get fiat money after it will be traded to local exchange. In this way there is no need for one to bring more physical money as bitcoin could unify all fiat money around the world as trading pairs.
It's definitely an interesting thought, it's something that I've thought about in the past as well. What if I could just carry a USB stick with my bitcoin wallet instead of cash or even credit cards when travelling around the world?
I think that it's already possible, given that you are willing to convert your BTC to local currency at each of the countries you visit. That's a tiresome process, but it can be done through platforms like Localbitcoins quite easily.
Though, in the future, we may see bitcoin being accepted directly instead of indirectly through having to convert it to fiat first due to the rise in merchant numbers. Even then, however, I wouldn't call it a "unified currency for all fiat currency". It's just an accepted global currency at that point.