"...how you guys cook it in the field?
I mean do you do exactly the same thing as in use a fry pan, or do you fashion some sort of oven out of foil or simply put it on a board in front of a fire?.."
I think in one of those Ray Mears Tracks links he uses an upside down cooking pot, put the bread in the lid, put pot on top of lid, place in embers, maybe put some embers on top (line the lid with flour to prevent sticking).
I have managed a few times to make a scone sized loaf in a crusader cup with a lid, lay it into the embers on its side with the handles upwards.
Edited to add:
Obviously you could fashion a makeshift wooden chopping board from bits of fallen tree branch and such, however I would recommend the
Ikea 'DRÄLLA' chopping board (£2 for two) which is made of light bendy plastic, take a pair of tough scissors to it and cut into smaller pieces, you should be able to make a small rectangle which will roll up into your billy can, I find these invaluable for preparing foodstuffs when I'm out and about.