This is a cute idea- you could modify it- instead of using small plastic bottles- if you save baby food jars- you could use them-
the morning after a nights campfire- scoop some ashes into the bottle and label it! I think my youngest would love to do this!
Here is a link
Camp ashes

"life is about sitting around a fire with a mountain pie maker"
+2002 Coachman Captiva+