Let me modify the question a little.
They're boys! They will not carry anything big, bulky or heavy for a day hike. They only have their CamelBak because it has easy to carry water.
The boys have a watch cap, a military style poncho and leather work gloves. So they have something to keep their head warm and a wind and rain layer. I am wondering what I could have them carry in their pack that would help keep them warm if they have to spend the night. They all have a medium size CamelBak backpack so it can't be too bulky. They are 15, 12 and 12 years old.
Hi Craig_phx
For lightweight compact insulation the Piqolo down pullover from PHD Designs may be useful at 11.7 oz but may be a bit over what you would want to budget,
available at
http://www.phdesigns.co.uk/product_info.php?cPath=25_59&products_id=114options are available at added cost for stud on down hood and more waterproof materials using Drishell. This is one of the lightest and compact jackets available for the warmth they provide.
I would forget about fleece for insulation, being to heavy and not really warm enough and also doesn't compact down to well.
For a cheaper down jacket at around 18 oz the Filium down smock
available at
http://www.alpkit.com/shop/cart.php?target=product&product_id=16287&category_id=248is considerably cheaper.
If down kit is not acceptable then something like the synthetic Snugpak Softie or Nanok SF range Jackets will be much warmer and compact than fleece.
http://www.snugpak.com/30_codegreen/32_01_sleekaoriginal.htmhttp://www.nanoktactical.no/These jackets are rated about 5 degrees Celsius warmer but will be about 10 to 12 oz heavier than the Piqolo down pullover.