We cannot give you a definitive list of what to
carry with you. Different people have different idea's about what to
bring, ask 10 people, you will get 10 lists. One thing is for sure,
although you sure don't want your pack to be too heavy, you don't want to be
without a need item either. We are going to present more than
one idea for packing. Become familiar with the items and why you might
need them. Then learn how to pack smart. Packing too heavy on your
person leads to comfort and even safety issues as it can increase difficulty
with operation. Packing something on your sled and loosing access to
it is dangerous as well. There is no one way to pack and there is not one
list of what to bring.
The needs for some things is always obvious at
first: like extra sun glasses is for snow blindness, needle and thread is to
repair a critical rip in clothing and tie rope is for building a shelter.
There are courses and resources on what to do
with a lot of this stuff.
Many people pack different for different
conditions. Local riders usually keep more stuff on the sled, especially
the heavier stuff - since when riding local there is a low risk of loosing
complete access to your sled (at least not everyone in a group). When
people switch to mountain riding, things change - everyone can loose access to
all their sleds in a flash, or you can be lost from the group for a day - people
pack more on their person.
Some people pack their back country pack and they
take it with them all the time, especially when they are in and out of the back
country often. Some people carry duplicates in the sled, so they can leave
the back pack at home for local riding. One thing is for sure, if you
switch things back and forth one day you may loose track of something that could
have saved you - duplicates can be safer. Also, many people find it a real
pain to go digging in the back pack for something
Tri-County Day Back Packs
Check out Traffic Safety in Alberta's packing check list:
http://www.saferoads.com/vehicles/snowmobile_snowchecklist.html
Here are a couple of lists that were in a discussion thread on
Snowandmud.com on what to carry in the back country - more comprehensive than
the above:

From FARM_BOY
OK here's a list, it's alot of stuff, but use any of it once
and you'll be glad you had it, even if you "borrow" it to someone else it's
worth it:
Beacon
Shovel
Probe
Garbage bags
Flagging tape
Phone (its rare that they get reception but what the heck)
Candle
Saw built from old Chainsaw chain cut in half with bolts welded to each end for
handles
Matches in 35mm film case and lighter
Small tarp
Space Blanket
toilet paper
LED headlight (straps to your head instead of a flashlight)
Spare batteries (for GPS, Beacon, and flashlight/headlight)
Camera/Video cam
Spare sunglasses (snowblindness sucks)
Spare clothes: Socks, sweaters, touque, mitts, gloves
Heat pads (the ones you break and they provide 8 hrs of heat)
Tums
Advil and asprin
Food: Dried goods, Jerky, Boullion cubes
Tin Coffee cup (can be used to melt snow, make soup etc)
Tampon (makes good fire starter)
Water
Alum foil
First aid kit
Whistle
Snowshoes (small aluminum ones)
Cumpass
GPS
Knife
Zip Ties
Tarp Tape (Not duct tape, it don't stick in the cold and tarp tape is way
stronger, and it comes in 4 colors)
Spare nuts + Bolts
Tow rope
Maps
Climbing rope (this stuff is tuff has many uses and strong as heck)
Mech wire
Small roll of 14ga elect. wire
Gas antifreeze
Tools: Assortment of Wrenches, cresent, vice grips, etc.
Electrical kit: Has Elect. tape, wire strippers, conntectors etc.
Ratchet straps
Small hatchet
Extras:Spare Belt
Small bottle of coolant
Small bottle of synthetic 2 stroke oil
5 liters of fuel
On the want to get list: Spare beacon, Spare probe, Altimeter, BIGGER SLED to
haul all this stuff................

From 2003Summit
I don't know if anyone got the large orange plastic bag, I
like that one (just remember, not head first!)
The survival guide is also a handy one, and paper and pencil.
Whistle
Compass
Extra Socks (in a zip lock bag)
Survival Kit (in a zip lock bag)
Survival Guide
Emergency heat reflective blanket
Large orange plastic bag "Crawl into it to keep warm, plus is highly visible"
Water Proof Matches
Fire Starter
Good LED Flash Light
Multi-tool (pliers/knife)
Some Tie Wire
Hatchet
Survival Knife
Powerbars and trail mix
Spool of strong thread and a few needles
Roll of Toilet Paper
Note pad and pencil
5 hour candle
Orange Trail marking Tape
Spare Compass
Tree Saw
40' nylon cord for tying
Plastic Bags (safeway sized)
Aluminum Foil
First Aid Kit (in a zip lock bag)
Advil or Aspirin
Tums
Blanket (in a zip lock bag)
Sun Glasses
Extra Toque & Gloves (in a zip lock bag)
Stainless Container for melting snow
"High Quality braided 3/8"" nylon rope 50'+
Avalance Probe
Avalance Snow Shovel Scoop
Avalance Show Shovel Handle
Spare Water
Tool Kit
Electrical Tape
Zip Ties
Spare Nuts and Bolts
14ga Electrical Wire
Wire Connectors

Someone posted: extra headlamp blubs: you never know how dark
it is till you loose one.

Also, there was a tool and light post from 2003Summit
All tool stuff is in the sled (the tools are heavy).
This might make you laugh. For tools I have a 1/4 socket set, a 3/8 socket set
up to 19mm, a 3/8 deep set up to about 14mm, stubby 10, 11, 12mm wrenches,
serious pliers, serous needle nose pliers, vice grips, a 3/8 ratchet, set of
allan wrenches, all the screw driver bits you can think of, some extensions
(both 1/4 and 3/8) and a 3/8 U joint, a 1/4 to 3/8 adapter. It weighs several
pounds. I don't feel good about thinning it down either. I think I also tossed a
spark plug socket it there too. There will be one day when I need something that
will make years of carrying it worth it. The other nice thing is when I wrench
on the sled at home I just pull that out and I have everything I need (nearly).
Most of the other stuff is really not that big. The spare toque, blankie and
gloves are about the biggest things.
I haven’t carried spare batteries on the sled. I rent beacons from cycle works,
they have SOS, the battery low indicator seams to come on days before the
battery is really dead so I haven't been too worried about them failing me on
the hill. I bring spare batteries but they stay in the hotel. I guess though if
one were to get stuck on the hill for a few days though it could be a problem.
The only other item I worry about is the flash light, but it's LED and I don't
worry too much about it, change them every couple of years. I do keep two LED
flashlights though, I worry more about loosing one or it just failing all
together (or getting crushed or something). More than anything I would hate to
be stuck after dark with out a very good flash light.
Speaking about LED flash lights; MAG finally has a new 3 watt 2AA LED
flashlight, a replacement for the MAG mini. It supposed to put out about as much
light as a 2D but last 45 some hours continuous. Can be had from MEC for about
$21. Just to give you an idea, those blinding white LED flash lights are using a
0.5W or 1W LED, 3W LED is big light.
I also carry an GMRS radio, it's usually in the windshield bag. It's
rechargeable and the battery will last about 3 days as long as you don't talk
all the time. Like in this post...