I would trade the space blanket for an Adventure Medical Thermo-lite-2 bivy sack or similar.

Here's my list for my 5-year old:
backpack
bandana, red
bear-bell
Bivy Sack AdvMed
BUFF neck-wrap
energy-bars
flashlite AA
Garbage Bags, Orange
hat
jersey or light fleece
LED Turbo Turtle, white
lightsticks
Rain-shell w/hood
socks
Sunglasses
toque
toy, his choice
water, 1 liter
Wet-Wipes, softpack
whistle