per jason's request, a breakdown for texturing of barrel and gas can
here is barrel mesh unsubdivided. the blue edges are seams that i have marked. simply select the edges you want to mark as seams and then in your UV options, select "UV Seam Toggle"
barrel subdivided to level 2 (uv seams will disappear on subdivision, fyi)
once seams are marked, select UVs Unwrapped, then select Unwrap UVs, and you will see the unwrapped faces appear in your 2d and 3d uvw windows when you open them. then simply export your uv's to image.
then i open the uv's in photoshop and start placing/painting textures over the uv's. not quite visible, but i usually place the uv layer on top and set the layers blending mode to "multiply" so i always have the mesh laying over everything while working on the textures. (yes, i could have easily just created a simple barrel primitive and created one uv chunk for the object, but this is the road i went down

)
save the map and apply to image slot for material and assign to object.
same process repeated for metal barrel bands and barrel lids...
the gas can posted previously was done in a sloppy fashion as i mentioned, so here's a quick re-mesh showing a few parts of the process that were left out in mapping the barrel.
same as before, although i've refined the subdivision on this one for a better unwrap. mark seams, hit unwrap, and you've now got your uv pieces displayed in your uv windows.
the biggest uv piece shown is the part that belongs to the handle which is obviously not larger than the body of the can on the modeled mesh. select the object and "scale uvs proportionately"
then "arrange uvs to bounds" will line everything up for you in an orderly fashion.
next, i want the bottom of the container to show up as one uv chunk instead of two as it is shown so it's easer to paint/create map for and avoid noticeable texture seam.... obviously
select the edge that both uv parts share
in the uv tab, select "Move and Sew" and it will sew the two pieces together
one last thing you can do to improve the uv's is to relax parts of the mesh using the smooth brush.
select the object and enable your smooth brush, then smooth out parts of the mesh as you see fit. you can find some standard uv checkered maps on the web that you can apply to the object to see how straight areas are before doing so as well, which can help out in some cases.
i am by no means an expert on any of this, just sharing what i've dug up trying to learn the process myself. hope this helps

i know there's also a correct term for the uv pieces, but like calling them chunks... reminds me of my favorite character from the Goonies...