Well having done more than 5 solo trips I am qualified to answer this question.
There are many options:
Selfie: Probably the most obvious one, and you weren't looking for that I believe.
Time on my DSLR: Place my DSLR on either the tripod or a stand or a flat surface and click by setting a timer.
Ask a stranger: The simplest one, I ask a stranger (preferably someone shooting with a camera) to click. This helps with two things, one is befriending someone new and getting a better picture.