I just didn't figure out for what I should use the back pocket, it is too small for the iPad and you can only put thin stuff into it, because otherwise it is going to bulge and doesn't look as nice anymore. I also haven't found any use for the two front pockets, but I think this will resolve itself over time.
I put my wallet in my back pocket. but I also have a one of those long and thin zip-around wallets. I like having easy access and not having to fish for it among all the other stuff thrown in the main compartment. it's the same thing I do with the back pocket of my ps1. I haven't used my pilot bag to travel yet but with the ps1, I love sticking my passport and boarding pass in the back pocket when I'm leaving a plane and will need to get it out several times for immigration/customs/security, etc.
I also haven't ever put anything in the front pockets yet. I'm thinking stuff I don't use a lot like headphones and travel tissue packet.
my favorite thing about this bag is that it's super light. I use it when my arms & shoulders need a break.