I might as well explain my solution: I use the D-RES 50AW from Lowepro with an extra Lowepro hip belt. I do cross the shoulder belt over my right shoulder from left of my belly front to behind my right hip with the bag in my rear. It swings freely to the front along its belt.
I use it when walking, travelling (often with a small top backpack). I have changed film and or lenses with this bag on a foot wide fallen tree log across a raging creek below, This is very small as a bag goes, very light, very compact. 23 cm wide, 12.5 cm front to back and 15cm deep.
It carries my G2 with any one lens attached and 4 other G lenses: 16mm f/8, 21mm f/2.8, 28mm, 45mm, 90 mm; the TLA 200 flash. All lenses have hoods and UV filters and caps attached at all times for speed; a small brush, microcloth, string monopod, extra CR 2 batteries, extra lens caps, film, ..
I separate the inside into three compartments: 90mm right side back towards my body, upside down, fully mounted with filter, hood, caps (just comes in at 15 cm tall); in front of it is the 28mm lens above the flash. All of these have velcro soft dividers between them. On the left side I carry the Hologon and its finder, as well as the 21mm finder in their pouches in the back, close to my body. The Hologon 4X filter sits left front bottom in its pouch, accesible from the center of the bag. On top of it the 21 or 28mm lenses, whichever. The 21, 28, 45 lenses all have about the same size with their hoods on and can be interchanged in bag position.
The camera (G2) sits with lens attached in the center between velcroed soft dividers. It sits face down with any lens (plus its hood) of focal length exceeding 20mm. I can keep one finder on the hot shoe at all times. If I keep the Hologon on the camera, it slides right intro the space vertically with its finder on.
I wish the bag was maybe 1cm larger in each of its three dimensions, but i have not found a 25cm by 14cm by 16cm bag anywhere and this fits perfectly small, snug, safe.
This configuration takes a few small vecro pads from Lowepro which Maury Cohen send me free of charge when I requested them from Lowepro.
The messenger bags mentioned above are soooo big, though they may be useful. They are tooooo biiiig for me and my taste and the way I work.