For trips longer than 5 days, I add a few items to my first aid kit (more antibiotic ointment, more sterile pads, etc). I also make a quick calculation to see if my MSR Pocket Rocket + fuel can combo will end up making more sense to bring than my Esbit stove and fuel tabs. The Esbit fuel tabs weigh 0.5 oz each, and it takes one tablet to boil water for one meal. 2 hot meals/day, 8 days + 1-2 days reserve, 20 fuel tabs = 10 ozs. If more cooked meals are needed (cooking for more than one person, etc) or the trip will involve extreme weather and high exposed camps, the trusty old MSR Whisperlite starts to make more sense.
For snow camping there's no choice, of course - if I'm going to be melting snow for drinking water, I want my Whisperlite!
So to summarize, for 6+ Day Trips: