Besides the K-Seal, I also picked up a $10 drain pan, some antifreeze/coolant, a bottle of radiator flush and availed myself of the cheapest motor oil/oil filter combo special they offered. I also stopped by a Wal-Mart and picked up a coolant flush kit for 4 bucks, along with a couple gallons of distilled water. This is basically a T- valve that you insert into the one of the coolant lines, with a backflow preventer. It comes with 3 different valve sizes to fit various size lines and 2 metal hose clamps to keep it on.
I noticed that they make non-poisonous antifreeze now, which I wasn't aware of before, but it was more expensive, so I just determined to be careful and picked up the poisonous stuff. You can get the kind that is premixed (you don't add water) but it is slightly more money, and I would have needed two bottles. So again, I went the cheap route and bought a single bottle of the coolant that you mix 50/50 with distilled water (since distilled water is less than a buck a gallon at walmart).
First I drained as much of the coolant as I could, which was more difficult than I expected, as the 2002 GMC Envoy ( which is basically a Chevy Trailblazer with different trim) doesn't have a radiator drain valve! Some folks online claim it actually does, but I looked and looked and could never find it, so I just loosened the hose clamp and removed the hose from the bottom. To make sure I was draining as much as possible, I also jacked up the rear of the SUV.