Get a couple of packs of these Plastic Screw-Top Sample Tubes
You can likely just get them at a crafts store.
I use[d] them all the time to take pre-measured charges of back powder to the range for cap & ball pistol competition.
Once filled you can just throw them in a bag/your pocket/anywhere and they're secure -- and you can see the levels are the same.
No brainer (perfect for me)