Bootable MacOSX 10.6 Snow Leopard emergency USB flash drive boot disk

Disk Utility should be able to do the task. Exactly what won't work that worked for Tiger and Leopard?

Most uncheck what they don't want installed, then afterward use CCC to clone but not copy most of the applications they won't need, but retain the 3-4GB of hidden files that are essential.

Then test that. And if you want, don't clone the man pages and such which could be optional.

There are threads on trying to put SL on 4GB flash SDHC. Not 2GB.

It would be nice to be able to make a bootable 4GB DVD.

Not something I really know about, but it seems to me that a bootable DVD would have to be specially constructed for this purpose, as is the case for an OS X install disc and various commercial products. I don't think you could just install OS X onto an external disk partition, clone that image to a DVD, and then successfully boot from the DVD, even the image was small enough to fit. When a "normal" version of OS X boots, it expects to write to its startup volume to create caches, swap files, configuration files, etc. It could not do so if the startup volume is read-only, as would be the case for a DVD.

Why not just use a larger USB flash drive?

I found this article:
[2009 Live DVD, howto make a simple, working osx livedvd|http://www.insanelymac.com/forum/index.php?showtopic=144128]

Here's the overview of the method presented there:
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How it works:

This method works because OSX has a disk image boot system in place to support its network boot system. IOHDIXController and kernel can take a path to disk image supplied to them, and mount it as /, via "imageboot", which recognizes a disk image as an attachable filesystem.
Further, Apple has setup a system to take a read-only disk image and attach a shadowfile to it, so that it is writeable. Intended to support a network boot system by making the user's session local and non-persistent, it is implemented in /etc/rc.netboot. Basically, vndevice (/usr/libexec/vndevice) attaches a shadow file to the dmg, and enables a copy-on-write strategy on that device--writes to the dmg are diverted to the temporary shadow file. This is much like what happens on a linux live dvd, albeit with Unionfs.
Normally the shadowfile is created on a local disk or network share, on either nfs or hfs. Under my method, the shadowfile is created on ramdisk formatted with hfs, and the system behaves exactly as if it were booted with netboot. The difference is that I specify that the dmg to boot from is local( file:///), and then manually start a customized rc script. The script behaves like rc.netboot, except i create a ramdisk and setup the shadowfile there instead of on a local disk. After that / is R/W and OS X boots normally into finder...and beyond.
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Got that?! 😉 😉

Well, I actually posted that mainly in jest (complete with winks) as something much too complex for most users (including myself) even to contemplate, but if you think you can make use of it, more power to you!

Alternatively, try DasBoot at http://subrosasoft.com/

Also, Snow Leopard. Good computing.