Panopticon: welcome!

I used to do a fair amount of backpacking, including thru hiking the AT. For a combination of light weight yet good coverage and IQ I would suggest a wide fomat zoom, a mid range prime and a telezoom. I primarly shoot sports and events and my entire lens collection consists of a 17-40 F4, a 50mm 1.8, a 24-105 F4 and a 70-200 2.8. The only IS is the 24-105, personally I hate IS but thats another rant. I have a 5D Mk I and a 1D Mk II (now with over 300K clicks!). I love the range of the 24-105 for bopping around town and general travel photography. The 17-40, 50, and 70-200 f4 non IS would be a good lightweight full coverage option for you that wont break the bank either if you buy used (another thing I always do)

FYI, for a widey wides to really pop you need to get up close and personal with the subject.

Good luck!