I really like Frau Fowler tooth & gum powder. You can find it at Whole Foods (and probably Natural Grocers, Sprouts, etc.) and it last me at least 6 months...you just need a small sprinkle on a wet toothbrush.
Then I use those tiny nalgene bottles from the travel section to store it. Super lightweight!
I love that the original container is in a recyclable container rather than trying to track down a terracycle center/box that takes toothpaste tubes.