One word - Cache.

If you plan on never coming home again, there must be someplace you intend to head to. If I was Backbreak Bob here, I'd cache ammo in several out of the way places along intended and/or probable routes.

As to pack weights. I routinely averaged above 90% on my PT scores. I maxed the run for 21 y/o on my last PT test (I was 42). I had rucks go from nearly nothing (summer at Bragg) to well north of 100 lbs (aforementioned Alaska trip, to include radio). If I had my druthers, I'd carry little more than food and water with gotta haves, and rely on pre-place caches to supplement.