In Neptune's Brood there were "slow" currencies where transactions had to be settled by communication with other star systems. It was created as a deliberate way to drive colonization of new star systems, since the only way to create more of it was to colonize more systems. The founders of a colony could end up quite wealthy, if they survived the attempt.
Of course, for every-day transactions there were also "fast" currencies where transactions were settled more or less instantaneously, and "medium" currencies where it would take longer but still be reasonably quick (probably for transactions between parties on different planets in the same system, but I don't recall that it was specified exactly).
Since I won't have time to read this book for at least several months - what are those colonists able to spend their newfound wealth on? Goods that will have to travel from lightyears away?
There is some physical trade between systems in the book (it's cheaper once you know you won't have to build a civilization on the other end), but there's no real enumeration of the possibilities in the book.
Given the characters seen in the book, I think founders mainly try to set themselves up as president for life of some planet or moon in the new system. Another example shown in the book is emigration; once you're sufficiently wealthy you emigrate back to some place nice where you can enjoy it. Of course that requires building a starship, which pretty much requires setting up a successful civilization that can support a starship industry.
Of course, for every-day transactions there were also "fast" currencies where transactions were settled more or less instantaneously, and "medium" currencies where it would take longer but still be reasonably quick (probably for transactions between parties on different planets in the same system, but I don't recall that it was specified exactly).