We live at a time when "I have nothing to do" is a really bullshit excuse. You have the whole internet available!
- learn languages (e.g. Portuguese, Russian, Chinese, Japanese, Arabic, Spanish - to cover most of the world's population)
- learn new stuff (statistics/machine learning, quantum mechanics, chemistry/biology, philosophy, programming, ...)
- do crowd-funded science (https://www.zooniverse.org/)
- help with open source projects (they need both programmers and non-programmers)
- teach people English (or any other language you know)
- entertain yourself (chat, watch movies, read books, play games)
Even for older generations, who might not be so comfortable with technology, there are plenty of useful things they can do in the real world.
- mentor kids
- tidy up parks and other public spaces
- participate in or organize hackatons/hardware hackatons/makerspaces
- experiment with learning/science/research in your home (make a spice garden, grow plants using hydroponics, prototype using 3D printing, redecorate your home with cheap materials)
- hang out with lonely (often elderly) people
- (learn to) cook
- work out (bodyweight exercises - you'll live longer)
I seriously cannot imagine ever being bored with nothing useful to do (except when I get home after work, I'm tired and I only have an hour or two of free time, so there's not much time to start anything meaningful - but even so, I spend a lot of time programming my personal projects).