I followed a suggestion on BPL last month and got a 2.5 oz "Sea-to-summit" daypack off of ebay and I'm going put a few more miles on. I've used it (carefully packed) for some miles last week.
I'd bag the mirror and lighter and knife and whistle - It's the main trail corridor:
North is one way, south is the other.
Need to get a message out? Tell a passing Boy Scout.
Need to start a fire? Rub two Boy Scouts together.
Need to trim a blister patch? Bring small scissors, not a knife.
Of course, most of it is water and food, and while there is water further on, don't scrimp on the food. I've got many 40- and 50-mile days under my belt of successfully gulping water at water stops and carrying relatively little, but YMMV - my wife's certainly does. But 2.34 quarts - more than half a gallon - seems heavy to me for April on a fast-paced trip, but I'll be slugging down a quart whenever there's water. -David
Editted to participate in the Great Sock Debate: My standard is a pair every 10 miles. I'd be doing laundry on a thru-hike, but changing often (and having options) has helped me on the 50-mile days. It also might allow you to forego the weight and heat of the gaiters. I HATE pebbles in my shoes, but slightly higher socks and much more frequent changes have been my solution.