You can easily snowmobile beyond immediate help, so basic repair and survival kits, expandable for longer tours are essential.
The Repair Kit should contain:
spare belt
spare spark plugs
manufacturer's tool kit
extra wrenches
nuts & bolts sized for your sled
tow rope
pry bar
duct tape
wire
extra ignition key
work gloves
An Emergency Kit should contain:
First aid kit
sun block
sharp knife
saw
axe
map
compass
mirror
waterproof matches or lighter
flashlight
whistle
aluminized blanket
high energy snacks
extra clothing/socks/mitts