cheapie round white plastic palette. Available at Michael's/AC Moore etc, about $1+/-. They have 6-7-8 wells and a nice flat space in the hub to mix/blend on. When dry the acrylic paint can simply and easily be scraped off for further use. I used to do what you do but being the slob that I am the accumulation of paint mixing vessels got out of hand.
For enamels and oils I use waxed pages from palette paper books (simple wax paper basically, wax paper clipped to a small small clip board will work. I do like to mix my colors against white simply because I can see the "color" i'm working with in a more "pure"/clean form ( I won't get into color ambiance here:)
I mix washes/glazes (filters) in bulk usually and those I do in cleaned out paint and glue bottles, bottles that have an additional liquid cap seal. If it just a small wash-glaze I will mix that in a small metal palette as described above or whatever is close and will hold a liquid (that slob thing again:))
Basically take $10 to a craft store like Michael's/AC Moore (if in the US-sorry my assumption that you are) and you'll be able to get palettes for life.
ps I agree with you I would scratch the pouch (which I had no pics of at all) that Andy sent you. It's visually more interesting and it's brown, which I find more fun to paint.
All the one's I've got pictures of are like the map cases you describe.