I use the Addis 330ml beakers availible on amazon. They partly stack into each other but hold 2 to 3 scoops of powder. They also allow the powder to be tipped directly into the shaker with no mess.
I’ve succesfully (re) used small zip-lock bags (sandwich / freezer) for travelling which I place inside a shaker along with blender ball in my luggage. Works a treat.
Promixx are ok but not enough liquid capacity for me. I like a big 'ol drink of Huel.