The specification is at least as bright as a 2aa minimag. I'd put that at about 8 lumens, let's say 100 mA to a reasonably good led, or about 1/3 watt. You really want to carry a 6 battery light every day?! I'll presume that means six AA-sized cells and not six D's /ubbthreads/images/graemlins/grin.gif. Lithium AA's are about 4 WH and six of them would be 24 WH, so 72 hours at 1/3 of a watt. Let's figure on a Downboy-like converter with some switching loss, so maybe you're in the 50 hour range. With alkaline AA's, maybe 30 hours, but much lower running costs.
More practically, the light you probably want is a Tektite Expedition 300 which has six or seven 5mm leds and runs on three alkaline C cells. It's about the length of a typical 2D household flashlight, but thinner. It will run 12-15 hours at good brightness followed by 100+ hours of gradually diminishing brightness below the Minimag level.