Good lord that looks like a lot of hard work. Hauling around buckets of rock and dirt is no easy thing on the body. You must be in very excellent physical condition.
I like the way you make use of the things that are by products of one project in order to further another project.
This reminds me, I've gotta go redig the hole for my mailbox post and pour some concrete in it and re-position the post so it doesn't lean so badly (it's been hit by cars twice in the past year). Work work work....
One thing I'll point out is that if your mailbox post is wood, you may not want to pour concrete around. Since concrete doesn't absorb water, more actual ends up in the wood, which can cause it to rot more rapidly. If it is a metal pole though it won't matter. Just a thought, if you don't mind the advice.
I'm getting there! Options are limited.
Hey thanks for the advice! I'm always open to learning from others. The post is wood actually so maybe I'll reconsider the material I use to support it. That makes sense as I once learned you can't put a wood floor on top of concrete slab because of this very reason (the moisture issue).
Perhaps filling the hole with a mix of gravel and dirt would be a better option for long term stability (or maybe I should just get a metal one and use concrete with it as you suggested).