For carrying my Tech V around the city, I usually just carry it over my shoulder, or switch to around the neck when I'm shooting more actively. I highly recommend the medium sized Calumet strap (the largest one short of a luggage strap) with the air pockets.
I had some belt packs made that hold 3 Grafmatics with a small pocket for small accessories or a pencil and pad by a guy who goes by "ted.b" on eBay. You can see if he has some up for auction or just e-mail him directly, and he'll make them to order. The price is very reasonable, and I think he's made some improvements to them since he made mine. Other options--the Ex Officio safari-style shirts have pockets that are large enough for a Grafmatic, and many coat pockets are large enough for Grafmatics.
A Gossen Digisix or Digiflash is a very compact meter for the field with this setup.
If you want a bag, I recommend the Crumpler Fux Deluxe with the photo insert, which is a messenger-style bag and has room for a full 4x5" kit. You could probably go with a smaller one than the Fux Deluxe, if you're not carrying too much. There's a Crumpler store in Soho (NYC, not London--are you in NYC like it says in your profile or the UK like your website?), if you want to try them out.