You really need less than you might think. The whole point of traveling is that you see something new. You're never going to know exactly what you'll run into or do. Trying to prepare for everything is impossible :). Living with limited resources is interesting in itself, and can even get you into cool experiences meeting new people you have to ask for help.
And as for the software, this is actually an interesting analogy. I don't think I pack my backpack much differently from how I try to decide what goes into a program. Whether it's bloated software or a heavy bag, I use 20% of its contents 80% of the time anyway. I could probably do without the rest and find some interesting alternatives along the way.
I guess it takes traveling frequently to find out you should cut on features :)