It's also worth replacing the tools in the standard kit with items that are made of actual steel instead of case-hardened cottage cheese. Decent spanners take up no more room than the standard gear and will serve you far better.

 

Honestly if you have duct tape , you don't need electrical tape.
What all you carry depends on what type of riding you do. Gravel roads thirty miles from civilization, maybe you carry more. Trails three miles from the truck, maybe you carry less. Some guys on here carry everything but the kitchen sink. For the riding I do, and so I don't weigh myself down too much, I keep mine pretty basic. I still feel I can , at least make it back from 20 miles out, maybe not with a full repair, but at least not be stranded.
Knobbie tires have a pretty sturdy sidewall, so you can ride on a flat if you have to . Zip ties around a flat or a rim lock will keep the tire from shifting around the wheel too much. I carry a front tube, it can be used on either wheel in an emergency. If you have a rear flat you can just stuff it in there, it will be twisted but it will air up and get you by.
Tire irons, a couple allen wrenches, needle nose vise grips, a cut down crescent wrench, spark plug socket, zip ties , tape, Small stick of instant epoxy, spare master link, razor blade, butane lighter. There may be a couple more items but it all fits in my camelbak (tube and irons are in a fender pack ).

 

One of my riding buddies carries a can of fix-a-flat. The last ride, he got a flat about 2 miles from no where. The fix-a-flat worked very well. It got us back to basecamp so he could do a tube replacement. I don't think you would want to continue on a ride without a real fix. Also, this approach would only be good if you had rimlocks, since it wouldn't help if you lost a valve stem.

I always bring my GPS on trail rides, so if I need to bail out, I can find a way back home. I use a hiking GPS (Garmin Oregon).

 

I found some zipties that are made from metal instead of plastic. I have been on rides where people have lost muffler bolts and the plastics ones wouldn't have worked as a quick fix.

 

I forgot to mention the small allen wrench needed to open the float bowl. You'll need one with the ball end so you can use it at an angle, thanks to the header. It's been very handy.

 

I have a piece of a wire coat hanger folded up

 

I forgot to mention a tow strap. If you're riding with someone else, sometimes it's better to tow your bike to a place where you can pick it up with a truck/trailer and take it somewhere more convenient to fix it.

 

wd-40

 

Compass ... I'm too poor for fancy gps at the moment.

 

Map and compass = no batteries req'd. Nice!