Reddit mentions of JAS : Empty Metal Watercolour Box : Holds 24 Half Pans or 12 Full Pans : with Fold-Out Palette

I dabble in urban sketching a bit, so maybe I can offer some input.

For pens, I use a fountain pen (lamy Safari) with waterproof noodler's ink. Occasionally I'll use semi-waterproof ink for interesting bleeding effects. Other options are microns and copic multi liners. For more dynamic lines the pentel pocket brush is great.

As far as sketchbooks I've tried the moleskine you mentioned, strathmore' s hardcover journals, and stillman and birn's beta, delta, and zeta series. The moleskine was okay, but the paper was thin and warped easily. The strathmore journal had a high cellulose content and didn't readily absorb the watercolor in my experience. The stillman and birn are my favorite, specifically the delta, as I loved the warmth of ivory paper. They also offer softcover and wire bound if those are your thing.

For a palette, I'd say it's going to be hard to find one that will fit both 24 colors as well as all your accessories. The tin you linked and other bijou-type boxes are better suited for limited palettes. This can hold that amount and you can probably stuff your water brush and sponges etc in the middle space. It has about the same length as the moleskine sketchbooks, so it shouldn't be too much of a hassle to carry around. Honestly, I don't think it's too big of a compromise to carry your brushes and stuff separately. I personally use this and cart it with all my waterbrushes, pens and stuff in a small zippered pouch. If you don't mind bulk, weight, and price, this could fit a lot inside.