I think of lightweight as just looking at things a little differently.
At it's very simplest, take a travel sized toothbrush but no paste; just use a little salt and and some rubbed up herbs found nearby. Rinse with water, use a steritab if necessary, so no need to carry lots of water. There goes 3kgs already. ( I live in west central Scotland.........about the wettest bit on the planet
, water isn't an issue, clean water can be ) Lightweight tarp, no tent, lightweight groundsheet, there's another 2kgs saved. Knife and folding saw are enough, I don't need an axe too, and I save another couple of kgs.......and already my pack is 7kgs / a stone lighter, and I haven't lost anything comfort wise.
I know that not all environments are suitable for this, and not everyone is prepared to go without all the bells and whistles and camping stuffs, but it's sometimes a good thing to really think about just how little you can capably and comfortably cope with.
Cheers,
Toddy