Easy answer: the ubiquitous GI Canteen Cup....available in aluminum or steel. Bombproof, cheap and easily found on eBay.
Better answer: I'd recommend that you carefully consider how you will cook before getting a kit. If you want to use a stove of some sort then figure out what stove and then find a kit of adequate size to allow you to nest the stove inside the kit. If your coking over an open fire try a billy pot (Zebra to be specific). As stated by earlier posters, Ti is awesome, aluminum is cheap, and to that I would add stainless, which is nice for open fires because it dissipates heat well and the soot cleans up easily.
My first choice now is a titanium Snowpeak 3-piece kit which nicely contains my Trangia alcohols stove with mini stand/windshield
