I haven't seen this idea posted before so here it goes: Considering the many shortcomings of moving a lot of cash between places far apart in two countries(theft, bad excahnge rate at local bureau de change, etc) and that credit card is not acceptable at every shop in every country, traveler's cheque would still be useful sometimes, however, companies like AMEX won't setup branches in every city of the world, and Paypal is not allowed by financial regulators of certain countries(like China)/So if a person A wants to travel to certain city where all the above-mentioned options are not practical, here is what he/she could do:
1.Arranging an agreement with a person B living in the destination city, who will pay person A an amount of fiat currency of the destination country upon receiving a certain amount of BTCs.
2.Person A travels to the said city.
3.Person A finishes the transaction with person B face-to-face using their computer to minimize the risk of a scam, and at the current exchange rate.
As far as buying use a exchange you get a better rate on a regular exchange compared to lets say localbitcoins. Also much safer using good exchange vs meeting someone.
I would not describe BTC as a travelers check at all. If you lose your travelers check you can call and cancel it. It's a little more like a credit card then BTC in my mind. Btc has more of a investment side then travelers checks aswell.