Since I mtbed before I started hiking, and also rode BMX and my 10spd before I mtbed, my older gear tends to be bike related, i.e. bike clothes, socks, etc. I have an old Cannondale water bottle that is from the 80s, It's got velcro around it and the bottle holder was simply a "half" cyclinder that has the velcro on it so the bottle would simply stick to the holder.
I also had my 10spd Ross Compact for a bit before I gave that to a friend. I gave my old BMW Schwinn to my nephew...
I also still use a pair of Diadora Jalapeno II MTB shoes with Time ATAC cleats on it to commute and bike tour. That was my first pair of clipless shoes and probably dates to 1995/1996.
Hiking wise, I'm still using my first pair of trekking poles, a pair of Komperdell ultralites from STP but that's not too old, just scratched to hell and one pole slightly bent. Maybe my Smith Sliders I use sometimes when bushwacking...
Jay