I would like to check the contents of a USB stick drive from a not-quite trusted source (my sister): is there a safe way to do this in OSX 10.9.5 or 10.10.1?


Question: Where to find ferry flights and empty leg flights?
Answer: Corporate/Business Aircraft

For corporate aircraft, this is a common occurrence and there have indeed been attempts to utilise these legs. A quick search on Google for empty legs turns up plenty of results. I came across two companies called flyvictor and returnjet that offered a bunch of flights from all spots in Europe.

Another similar possibility is getting a ticket for an extra seat on corporate jets that are not 'ferry flights' but simply have extra capacity. This article ("How to fly on a private jet for under $200 per person") might interest you.

Note:


They are 'opportunist' in nature. There is no guarantee a flight will turn up for your desired route, and/or there will be a return flight.
The company will always try and sell a flight like a normal charter if possible.




Commercial Aircraft

For commercial airlines, ferry flights are avoided as far as possible. They are (in principle) nothing but money down the drain. You will encounter ferry flights:


When you need to move the aircraft for maintence. 


British Airways run a facility in Cardiff for maintaining among others their huge fleet of Boeing 747s.
Austrian Airlines run a facility in Bratislava, requiring a 20-minute hop for aircraft due for maintence from Vienna. 

When stuff messes up, most notably breakdowns. For instance, an mechanical breakdown at a remote airport followed by ferrying the aircraft back once repaired.


The issue is that:


These flights are often at strange and/or irregular times.
Occasionally crewed by only cockpit crew and no flight attendants.


As such, there is little incentive for airlines to let passengers along even (if it may legally possible). The cost, time, paperwork and extra staff would most probably not pay off for the low number of passengers that could be expected.