I would suggest doing some BOSU/disc work, or training on any other type of “unstable” surfaces to prepare you for the terrain that may be involved in your hike:
I would alternate between endurance training vs. strength training. I would also include interval work as a part of your cardio training, really mixing things up.
Upper body work such as pushups, chin ups, TRX, planks, step ups etc. would be great since you’ll be carrying load on yourself!
Great idea about adding weight to your pack, it’s a good thing to adapt to this prior to going out into the wilderness and not being able to carry your belongings!
“Essential” elements that I would consider would be caridovascular training (both steady-state and interval) and a lot of flexibility work. Additionally, I would emphasis lower body strength work (e.g. squats, lunges, single-leg squats and presses). Lastly, I would perform a number of body weight exercises to enhance the ability to handle your own body weight as well as balance work to enhance proprioception.
I hope that this helps.
In addition to the above answers, I would add weighted step ups onto a platform to help build the strength needed to lift yourself and your pack up steep or rocky terrain. As well, it’s important to train for the downhills with eccentric conditioning of the leg muscles. Either train on steeper trails or use the stairs in an office building – I think going down stairs is a fairly close approximation. Definitely making sure the boots and pack fit well and are comfortable is critical – conditioning is almost irrelevant if the equipment makes you miserable. I have a client who occasionally wears boots and packs in the gym when training for a trip – I think any funny looks received had to do with their not realizing that some people train in the gym to better enjoy their time in the great outdoors. Have fun!
Lots of walking, in the hills. You train like you compete. Be sure to wear your backpack, loaded. Then when your backpack is not so loaded it will feel like a bit of the load has been removed. Kathie’s answer is great. Just be careful on the downhill, that’s the hardest. The negative, eccentric load on the quads can be significant. No big steps.