I know PhD is unsparing in terms of available time, but at times there may be situations that demand some extra income, for example, family situations or some medical emergency.
In such cases, are there any specific jobs PhD students could take up? This could be at some place within a university (a library, say) or somewhere in the city (assume it is a large one like London or NY). The desiderata are minimal time consumption and a sum of useful money which could be used to manage the unexpected expense.
Online tutoring and teaching - It can be less time consuming especially in the area of their expertise. Good instructors are scarce and they are online and offline companies that are always looking for quality instructors. Companies like General Assembly, [Udemy], Venturesity (sorry for the shameless plug :)) etc.