I used to go hiking with Nick. I used a child's size school back pack.......not the standard size, the smaller one for like the 1st graders! Perfect size.
I bought my zip panniers from the folks in the link below. Have used them a lot and they are holding up great... Got International Orange, because I want to make sure the hunters see me.
They deal in goats but they outfit a lot of mini's too.
They will even make you a saw buck to fit your mini.... great folks to work with.