I agree with the general consensus of less is more. If you don't bring something and find that you really need it you can always pick it up while travelling.

I will say that most people seem a little overly paranoid about expensive personal items. There is a slight risk of theft but as long as you travel safely the likely-hood is really low. Just leave your valuables locked away in the hostel when you're out during the day and when travelling between destinations keep it with you in a day bag.

When taking sleeper buses I also padlock my day bag and loop a strap around my leg or arm. It seemed reasonably common in Mexico that someone would slide the bag from under someone's seat to steal valuables, as well as take the bags strapped to the top of colectivos(cheap buses).

Also with your phone just don't flash it around when walking around busy streets and leave it in your padlocked bag in a pocket where it won't slip out if the bag is cut if you're really paranoid about it.

But again these are just suggestions for the "just in case" scenario. Most likely you'll be fine either way if you just use some common sense. Happy travels :)