Depends on how much juice you need. I have 2 spare batteries. And a battery pack. They serve different purposes and the batteries are very light. But for what you mention, I think a battery pack is a good idea. (But remember...when you're charging it's hard to use the phone...that's where the extra battery comes in.)
The bigger battery packs have become remarkably compact and can give you a ton of juice in a fairly small form. Here's the Anker that I use. What I like about it:
--relatively small for its capacity
-- Supports QC 3.0 quick charge.
--Quality company.
Anker PowerCore 20000
There is a 26,000 now, too, I believe. That is right at the limit of what airlines allow, so since I travel a lot, I decided not to push that issue, even if I am currently in the right. And of course they have some things that are more along the lines of emergency power that have a ton of capacity--but that likely won't be something you want to carry around while hiking.
I have a few portable chargers for business trips, etc. The 20,100 RAVPOWER one is approx the same height and width as a large phone in a case, though it is quite a bit thicker. That's probably my favorite one.