Found yourself stuck at Starfleet Command without enough credits for the sandwich shop? Yeah, neither have I, but even if there's the remote possibility such a situation could arise, this funky tool can help you avoid galactic embarrassment while fronting the cashier with all those captains and admirals.
Money In Advance's Sci-Fi Currency Converter allows you to convert conventional currencies to Federation Credits (Star Trek), Galactic Credits (Star Wars), Copper Stars (Game of Thrones), Bottle Caps (the game Fallout) and a bunch of others. As far as terrestrial coinage goes, only the US dollar, British pound and Euro can be exchanged, though if you're determined you can figure out the equivalent in Australian easily.
Each fictional currency is accompanied with a brief description explaining exactly how the rate is calculated. For example, here's the basis for Simoleans (from EA's The Sims games):
Taking three jobs as a benchmark (a paramedic, a high school teacher and a neurosurgeon) and calculating how much they earn per year in The Sims, we compared the results to average wages for these professions in the real world. We then averaged out the totals for extra, um, accuracy.
How useful is it? Not very, unless you're planning a trip into an alternate reality where such currencies exist. If you are, can you please let me know? I'd like to pick up a replicator.