I'm still debating this one myself. I've been getting by for years with a fairly standard stainless mug, plus a pot in winter. Kicked around some aluminum beercan pots but haven't made one rugged enough yet. I used to use Nalgene bottles alot, because I use really hot water from my Kelly Kettle, but have since abandoned them because of their weight and the BPA thing. So I am looking to carry two metal mug/pots with lids that can be used as a mug or as a pot but also as a water or hot beverage carriers. If I can get the lids tight enough I may trust them as hot water bottles also. I would like cozies for them also, and to fit in standard bottle carriers with the cozies on, but the cozies would be removeable, at least on the bottom, so I could heat them directly also. Perhaps a reinforcing band around the rim that also allows me to handle them when hot. Epoxied webbing maybe. I wouldn't mind if they were aluminum or titanium or even stainless steel as long as they were the right size. Something Nalegene bottle sized but only 800ml high would be about right. It's the lids I haven't quite figured out yet. Once I get something working out of aluminum I might look to titanium.

Something about this size, but with a cozy, insulated rim, and sealed lid...
http://www.backpackinglight.co.uk/product91.asp

I will first see what I can do with Foster's Beer Cans. I am not sure how I can get them to slip in and out of a water bottle holder while wearing a cozy, and still be rugged enough when empty. They weigh less than an ounce though, so I could add 3 ounces in insulation and reinforcement and still have a light pot. 4 ounces per unit is my target, including cozy, rim, and lid. Perhaps the water bottle holders need to be on the front straps. I don't really like reaching back there anyway. I could use the back pouches for something else.