This is an example of how I would configure extensions after a fresh System 8 install. I tossed in a couple popular extensions to show what I would and would not disable.

Some points of interest:

Notice that I don't simply turn them all off using the shift key on start-up, or use the "all off" setting in Extensions Manager. This would obviously turn off functionality that would want/need in the games I may be playing (for example the Open Transport networking and Quicktime).

Also, some of these items I have disable can also safely be trashed. For example, you can safely trash print drivers for printer you don't have (like all the StyleWriters) and extensions that I never enable (like ColorSync- I don't need it, I don't want it).

Without going one by one, let's hit some of the highlights:

1. Control Strip - Admittedly, this is a nice little "quick access" strip for some of the settings for your computer. The problem is that it fights to stay in front all the time (notice that it's front most no matter what program your in?) and this slows down the video for your computer. People who work with Quicktime regularly always suggest turning this off. Granted, most games hide the Control Strip, but I'd rather save them the effort, and not risk and possible performance degradation.
2. Mac OS Easy Open - Now this control panel just plain annoys me! How many times have you clicked on an "unknown" document only to have it suggest all the apps you know it's not, and not even list the one you want to open it with? This is one of the first extensions that get disabled on my systems.
3. RAM Doubler 2 - Yes, I am a RAM Doubler user. It sure beats Virtual Memory for speed, and I turn it on for my day to day work set. But just the same, when you know you're going to game, you must disable it. In some tests, it is just as slow as virtual memory. It will slow down your system for processor-intensive games (and in some games it's even noticeable).
4. Speed Doubler 2 - Nope, I never turn it off. No reason to.
5. Notice that I don't use Aaron, Kaleidoscope, or Aaron Lite. They look pretty, but they definitely slow down your system. At least disable them if you're gaming.
6. Other things I disable simply because they use up too much memory that I'd rather reclaim for gaming, such as Apple Guide, Desktop Printmonitor, FileSharing Extension
7. And others I trash right away because I never use them: Printer Share, misc print drivers, Speech Manager and associated files, ColorSync, Launcher, AutoRemounter, etc.

Why don't I have more disabled?

A lot of stuff in your System Folder are merely libraries (Library files are files that are referenced by other programs) that don't even load into RAM at start-up. They don't use RAM and they don't slow your system down by themselves. So you might as well leave them alone. Start messing with these too much and I've seen people who suddenly can't get any network access.

Other control panels, like the Startup Disk, Keyboard, or Monitors & Sound, are not really loading into RAM (or are only loading only a miniscule amount) that they are not worth troubling and are best if left alone.

This is way, in some respects, I liked the pre-System 7.6 Extensions Manager. It only showed you control panels and extensions that actually loaded into RAM, all others were ignored. I think this made it easier for non-savvy users out there.

Return to the Game Performance Tuning page for more details on this and other system performance tips (like how to configure individual control panels and modem tips). If you want to learn more about what individual Apple extensions do (i.e. whether you need them or not), be sure to check out Dan Frakes Mac Pruning Pages and InformInit.