When you can only take one lens?

I guess this depends upon the walk somewhat, but am curious to know which lens people favour if they are tight for weight and wish to only carry the one.
Information for bushwalkers from bushwalkers
https://bushwalk.com/forum/
Strider wrote:Samsung Galaxy S2...
Terrible!Clusterpod wrote:Strider wrote:Samsung Galaxy S2...
Whats the battery life on that one like?
whynotwalk wrote:If it had to be one, I'd go for my Canon 24-105L. Great from low light to portraits to landscape