Hikermor:

Carrying a very large pack when traveling at 40 to 50 mph is very challenging if the trails aren't smooth as glass. A good jolt from a bump and larger bag can bounce around potentially throw you from the machine.

We typically rent sleds (slang for snowmobile) and depending on the make/model there can sometimes be very little room to affix packs. Sometimes there will be room on the back deck behind the seat to bungee packs down and we can carry more. We don't know the exact model sled until we show up at the outfitter's location; we can only reply on knowing engine type and size, and track length and paddle depth. So we plan for no room on the sled. Most sleds will have some sort of compartment on the tail but they are usually small and we fill that up with extra two cycle oil.

I've fit most of the stuff on list in my pack on previous trips. I may upgrade to a larger pack for this trip though. I also carry a smaller front waist pack for quick access items (flashlight, jerky, glove liners, etc.)

Good point on the sleeping bag being a part of the FAK. Looking for something lightweight and pack up small.