For those who belong to a gym: 1) consider some of the classes in wright-lifting (called Group Power where I go) -- they provide an overall body workout; 2) consider yoga -- has been great for my balance, a critical need on rocky portage trails; 3) consider spin (cycle) classes -- builds both strength and endurance.

I also do the cycles, eliptical trainer, long walks, weights by myself. Fitness goes a long way to making a trip pleasant.