I have been using a combination of 75% baking soda & 25% salt for tooth powder.
The taste took some getting used to, but after a few times, I am used to it and it is what my family and I use on the trail.
Less than an oz of the stuff will last for a week or too.
I don't know of anything lighter.
I also carry a plastic tooth pick from Walmart (don't know the brand) that has one end that is feathered, which is great for getting between teeth in tight places.
Weight of a bunch of them is less than 0.25 an oz and I only carry one of them with me.
I also carry a disposable plastic flossing tool that has one end that is a tooth pick also, but not as nice as the one described above.
My tooth brush is a standard tooth brush with a cut down handle.
More bristles means more cleaning power, so I carry that….sure there is lighter options.
I have not used soap flakes, but I use soap sparringly in an old BPL dropper bottle. I find that I only need 2 or 3 drops to wash my MSR Titan Mug, few drops for washing my backside after digging a cat hole (Mike Cleland's Book Tip), and I do carry a microfiber wash cloth….few drops of soap in my MSR Kettle add water and I have a wash basin for myself with the wash cloth at night for washing my face, pits, arms, etc….sponge bath before bed.
For carrying some TP, I find that blue paper shop paper towels are strong and I can cut them to the size that I want. The extra strength of the paper towels means I can get maximum wipes per square and they are less likely to tear, rip etc….though, moving to the Mike Cleland's method of washing my backside with soap and water means I really don't need TP and I have found that my bottom is much happier with soap and water vs. TP.
Hope not TMI, but figured that I would tell you all that I know.
And yeah, embrace the hairless monkey that you can be and shave yourself down before a trip. :)
-Tony