Step 1: Turn Your Messenger Bag Into a Camera Bag
2) Buy a camera bag insert (such as: http://bhpho.to/1azyl3)
3) Put insert into bag...and, voilà!
Step 2: Materials Needed to Wax Your Bag
2) A double boiler. I recommend NOT using one intended for kitchen use...it can be a mess to clean. Rig one out of old pans, coffee cans, or whatever you may have around. I used two old, aluminum camping pots that I had sitting in the basement.
3) Wax. Many places recommend a blended mixture of paraffin and bee's wax, but I used straight paraffin, and it seems to have turned out fine. You can pick up a pound box of paraffin wax in the canning section of Walmart or your local grocery store. You shouldn't need more than one or two of the included wax bars. - LINK: http://bit.ly/fsoxAU
4) A brush. I recommend a bristle brush between 1/2" and 1"...up to 1-1/2". Any smaller and it would take to long; much larger, and it would be too unwieldy and messy. I used a half-inch artistic brush I had sitting around.