THIS GOT TOO LONG - I really ended up getting into this. Sorry friends.
I can't imagine myself being in this...uh..."predicament," but my sleuthier side makes me try to think about it.
The things I would consider (which clearly are not necessarily the things KC would consider) would be - not being observed, smell, physical discovery of remains, evidence to tie me to the death, establishing plausible deniability.
To be inconspicuous, I'd have to make it appear that I'm doing something that is not out of the ordinary (like taking trash to dumpster) or do it with cover of darkness, etc. I would try to do absolutely nothing to draw attention to myself.
The smell is so penetrating (especially if I were lazy/ignorant enough to carry a body around in my trunk for more than 36 hours) that I would realize that it would have to be disposed of in a manner that the smell would be sealed or hidden very well, or in a place where the smell would be masked by some other terrible smell such as a landfill, waste treatment facility or a stagnant marine environment (which always smells like death to me anyway and human remains might be mistaken for just another rotting fish or animal.)
The possibility of the remains being discovered would be diminished the longer I would wait before alerting anyone that there even was a problem so, after completing the deed, I would go into hiding for as long as humanly possible - not telling anyone and acting like nothing was worrying me - all is cool. This would also help with the plausible deniablility. Since I lived on a sheep farm for 13 years, I know how really difficult it is to dig a hole big enough to bury an animal (without a backhoe) and how deep an adequate grave has to be, I would not plan on burying a body with a gardening shovel unless I had opted for leaving the body buried in a sand dune someplace. I might drive to a poorly maintained beach area and take the body in a black trash bag to bury in the back dunes, knowing that it wouldn't raise too much attention and if I was confronted, I could be cool and say that I wanted to bury my kid's deceased dog. No one would ask to look in the bag and I could change my plan to a different location or backup plan.
Pitching a body - bound very well with something which would only decompose after the contents, with a relatively heavy weight (10 to 20 lb.) might be a possibility under the cover of darkness and if I was certain that the traffic would slow so much that I would not be noticed. However, the body's weight plus a 10-20 pound weight would be difficult to manage - 40 to 50 pounds. That is more than one of the really large bags of dog food at the grocery store (next time you walk down the pet food aisle, just drag one of those 40 or 50 pound sacks out and then try to get it back on the shelf) or a sack of feed corn. It would not be an easy matter to "pitch" it and so perhaps dropping off a bridge, but only if I was certain to be unnoticed.
The fear of being seen in an unfamiliar place doing something odd would probably cause me to look for a way to make it look inconspicuous like something other people are doing all the time. I would probably double bag the smallish body in lawn and leaf garbage sacks and just swing it up over the side of a dumpster, like I'm just taking out the day's trash. I might even carry a bag of trash in my trunk for credibility if a friend should see me doing this. <wink>
I would probably use the dumpster I ormally use - either at the apartment complex where I was living (Sutton Place or Sawgrass) or perhaps even setting it out by the curb for trash pickup (Hopespring.) 30 pounds in a bag stuffed with light paper trash (parents' receipts of someone unknown would be good so I could accuse someone else if the remains are found) might not be suspicious to the trash men. I would be certain that absolutely nothing traceable to me was in the bag with the body and would use latex gloves to handle all contents.
I would watch carefully to be certain the trash was taken without incident and then each day that passed, I would feel better and better that the remains would not be found and I would be more and more confident about living my normal life and telling a "kidnapping" story.
Hmmmm. Somewhere along the line here, I got distracted and started going to what I think Casey might've done. I know that wasn't the question but this was hard for me to think about . Sorry.