Quarterstaff,
For a single bladed folder, that I possess, I would rely on my Sebenza or SERE 2000 (less expensive). These and some other choices have already been mentioned. A couple of others I might consider would be my Gerber Paul knife, because it has given me a lot of good use over the years, and the Benchmade 940 (comment 1 on this one inserted below). The best bargain might be the Camillus EDC (see comment 2).
I only agree with part of your premise. Yes, in heavily used parks near urban areas, your rationale re: having a handy single bladed folder makes sense. You are, however, limiting yourself too much. No one, who would overlook your single bladed folder, is going to comment if you also have a multi-tool such as a Leatherman Wave, or a Victorinox Rucksack, as an additional backup. The Rucksack only weighs 3.7 ounces. If you are going to rely on a folder, it might be wise to have something in reserve. By the way, it is not single bladed, but the Victorinox Pocket Service Tool, has a one handed blade. The Pocket Service Tool SAK is heavier at 4.6 ounces. You can read more about it here:
http://www.bladeforums.com/forums/showthread.php?s=&postid=1423618
Personally, you now have your handy folder ready for use, a fixed blade unseen in a fanny pack along with your snack bars, ferrocerium rod, etc., wont excite much comment. It might be of questionable legality??? Considering this last, if you stand out for some reason, such as, have purple hair, carry around a beer bottle in your hand, dress in a ghillie suit, and have a nasty expression or like to get into fights, forget about also tucking in that sanitary snack bar cutter.
-----------Comment 1
I said this about the 940 somewhere else:
It is in a middle range for use. Light enough to easily carry. I find it a little long in the pocket sometimes in bending, and it can hit my keys, although it has not seemed to affect the finish yet. Mine is royal blue.
Knife blade seems fairly robust, but feel the aluminum scales could be a weak point for heavy use, if you torqued the handles heavily. The stainless liners should add some support. You have to give up something for beauty, weight, and price. The only reason I comment is the knife is so nice and the blade so functional, it lends itself to a lot of use.
Lest anyone feel that it would be lacking in a emergency, one might want to see the threads on the Benchmade forum regarding the abuse...errrr I mean use

that Sniper7369 put his Osborne Benchmade 940 through.
http://192.41.25.213/ultbb/Forum1/HTML/001584.html
http://192.41.25.213/ultbb/Forum1/HTML/001707.html
Great knife!
-------------------Comment 2
The Camillus EDC is a good basic single bladed pocket knife, that in its least expensive incarnation had a 420hc blade. I just read that steel has been discontinued, in favor of 154CM. I have and like the 154CM version, which is apparently going to be the standard, for the same suggested retail of $69.95, which means less on the street. It has a lock similar to the Sebenza. Further, like the Sebenza it is easy to clean. It fits well in a pocket, even clipped to my suit pants. The clip is great, but like all clips, it can get sprung, as happened to mine. The Sebenza comes with its own allen wrench so this is no problemand I probably had one anyway. The Camillus EDCs clips are held on by number 6 torx screws. A T6 driver is hard to findnone at Home Depot or smaller Sears. To be fair, at the smaller Sears, I checked, the sales person said I was the second person who asked, so he had ordered a couple. I kept wondering if that other person had a Camillus EDC.

Now if you want to spend more, there is an EDC with a Talonite blade.
I did find a T6 bit as part of a set on sale at a very large Sears tool section (in Sarasotaa one of the largest per the sales person). So now I have a nice new driver and lots of bits, also good for fitting in my Leatherman Wave tool adaptor. Some get the Benchmade torx set or other ones on the Internet.
If you wanted a larger knife, in addition to the TOPS mentioned (which is likely thicker/sturdier) there would be the new large Camillus CUDA MAXX 5.5 and the Rekat SIFU. Brian has a fuller version of his stories elsewhere on using the TOPS folder, and they make good reading!
I like taking my SIFU out for a walk, but note that the front of the blade has a ding in it where it contacts one of the handle pins. It is easy clean, in that it is open like the Sebenza and Camillus EDC. It is a good slicer, but I have gotten a couple of comments when slicing food with it, so it is probably not what you are looking for. After all, it is larger than several of my fixed blades. On the other hand, it does clip to my pocket.
I have not handled the Camillus CUDA MAXX 5.5 as it is not out yet, but should be out soon according to a post I just read. I dont think it will satisfy your needs for an unobtrusive knife though, and I quote: This is Darrel's original MADD MAXX, the 5.5" bladed bowie. Apparently, people notice it

Since I have them at hand, a couple of links are here including the imminent ship date in March 2002:
http://www.bladeforums.com/forums/showthread.php?s=&threadid=192121&highlight=max
and for pictures, including the lock area which also looks like the Sebenza, here:
http://www.bladeforums.com/forums/showthread.php?s=&threadid=188069&highlight=max
where I also learned of the 154CM upgrade becoming standard for the Camillus EDC.
_________Comment 3
Mike, now I know which model Pioneer you were talking about. Ill have to go back and check for original. I did see the number of different versions.
I feel a saw is very useful in a couple of areas not explicitly mentioned by you and Chrisaloia. If you need a strong sapling/branch as a walking stick, it is much easier to saw it off with a Leatherman Wave, SAK, or similar saw, than to cut it off with that type knife. Breaking it off will not work as you may get splintering on the end. This would also be true with one for a bow, although that is not what I was originally thinking of. It is also useful in getting a good strong baton to pound on things. For instance, breaking off the branches the Chrisaloia mentioned. I believe it is at
www.equipped.com that suggests that in an emergency, such a method is safer than using something sharp that might cut you. Thinking further, one might follow Christopher Nyerges, who carries a pair of Florian clippers as a more effective and safer alternative to shelter material gathering, etc., then a large knife. (Not as much fun

, but they are effective.) The only problem with clippers, apparently, is that everyone ends up wanting to borrow them.
