Holidaymakers heading overseas could benefit from a cash bonus due to the strengthening of sterling.
Four-fifths (80%) of the Post Office Travel Money's top 40 best-selling currencies are now weaker against sterling than a year ago.
Sterling's biggest year-on-year gains have been against the Turkish lira and the Russian ruble, the analysis of the best-selling currencies found.
There have also been big gains for sterling against the Brazilian real and the Costa Rican colon, the Post Office said.
But some other key European holiday currencies, including the euro, remain stronger against sterling than a year ago.
However, Post Office Travel Money said the pound is just 1.7% weaker against the euro year on year and it has been moving up in value in recent weeks.
It also said sales of some long-haul holiday currencies are already surging ahead of 2017 levels but a more cautious approach appears to be being adopted by consumers for some European currencies.
Sales of the Thai baht and the Barbados dollar are among those to have seen a jump.
Year-on-year sales of the Thai baht surged by 42% in the first three months of 2018, while Croatian kuna sales jumped by 32% and sales of the Barbados dollar saw a 29% increase.
Andrew Brown, the Post Office's head of travel money, said: "Sterling has been rising in value against European currencies in the past month and it may be that holidaymakers planning European trips are holding off changing money to see whether the pound rises further.
"On the other hand, the surge in long-haul currencies may be an indication that canny travellers are travelling to destinations further afield after reports of rising eurozone prices."
Mr Brown continued: "The appetite for travel to Croatia seems insatiable. Our kuna sales have quadrupled over the past decade, with no sign yet of a plateauing in demand."