I've just discovered potato flakes. They're similar to Deb, but better (ie, they don't taste exactly like fresh mashed potatoes, but are a lot closer to the real thing than Deb is - much nicer!).
And they're absolutely instant. I poured 2 cups of boiling water into 2 cups of potato flakes, then stirred, and it was ready to eat immediately (3 medium serves). I did stir through a bit of butter also, just to give it that extra creaminess and flavour that I think mashed spuds need. Replacing a bit of the water with milk would probably work well too, I'm guessing.
I found them at "Wholesome House" in Mowbray (Launceston) and thought I'd give 'em a try. They weigh almost nothing and cost almost nothing. They may be available in other shops too, but I've never noticed them before.
Now I've just got to think of something nice to go with them when I'm walking. What's good to carry on a bush walk that will go well with mashed potatoes (apart from surprise peas)?