I was taught and always start as full as I can manage but the description of your Saturday run is something I almost never see. Often it's two hours round trip for me to get fuel. Recently I had a member of our group break down and I was shuttling people/gear, it was four hours to get gas and 100 miles round trip because the pumps at Kennedy Meadows were down. If I tried to wing it on what I thought the day required I'd have been stuck. If your Jeep is kinda just used as a buggy I can see not filling it. For me I think the 50 lbs is worth the piece of mind, same reason I carry a spare. If I had a trailer at the trail head I probably wouldn't worry about that either.