Rinoa makes a great point about what she calls true love.
Indeed, I would die to save my wife or kids from death or some terrible suffering. That would be at the top of my list. Although, I worry the OP is vague on this point since it says "give up [...] your family". Does that mean give them up in the sense that I am dead or otherwise I cannot spend more time with them or in the sense that something has happened to them besides merely losing contact with me?
Grecorivera5150, makes a good point about -- in my own words and interpretation -- the way one who actually believes in an afterlife might be less likely to find heroism in living and dying for something. Like
Grecorivera5150, I also do not believe in a supernatural afterlife, so to ask me to die for something is a big request especially from a selfish perspective, presumably much bigger a request than to ask someone who doesn't really believe in death.
Spectrum takes an excellent philosophical look that questions that foundations of the question itself.
Sleeper1 also gives a good general answer, which is probably more philosophical than the approach I will now take.
I would like to take a slightly different approach and answer the question directly. As stated above my family is number 1, and coincidentally like
Spectrum I may really not be willing to die for anything simply because I selfishly want to stay with my family or want to keep them happy by not dying prematurely on them for some cause. Putting that aside though, imagining for instance hypothetically that I did not have a family or the thought experiment was otherwise restructured slightly to make the existence of and/or effect on my family moot, here are some of the top things I would die for:
- end world hunger and poverty
- end war
- end or nearly end rape and murder
- free all slaves, political prisoners and non-violent prisoners incarcerated for consensual crimes (e.g. marijuana possession)
- save humanity from extinction
- save the life of a child