Sometimes, the right tool is the one you have with you.
I had taken my flat black fixed-gear mountain bike to Moab so that I could ride with Carol and Colin, and stay at about their speed while still being challenged by the terrain. Colin was only 10, at the time, and Carol had not mountain biked on a regular basis in years.
One morning, everybody else chose to sleep in, so Carol and I headed up to Porcupine Rim. I knew that she would enjoy the view from High Anxiety Overlook, and that the out-and-back ride from the parking lot would be well within her skill level. But, when we got there and I pulled my fixed gear out of the truck, I saw that the bottom bracket was quite loose, and needed to be adjusted before we took off.
The only problem was, I had neither a bottom bracket lockring spanner, nor a pin wrench for the adjustable cup. It had been so long since I had ridden off-road with an adjustable bottom bracket that I no longer had those tools in my CamelBak.
I had a small tool kit in the truck. It didn’t have the bb tools in it, either, but there was a flat-blade screwdriver. I placed the tip of the screwdriver in one of the slots of the lockring and, using a rock for a hammer, knocked it loose. The tip if the Phillips screwdriver from the kit just grabbed the hole in which the pin spanner would have fit, and I was able to turn it and get the bearings adjusted.
Then, using the flat screwdriver and the caveman hammer, I locked everything back down. The bike was ready to go, and I didn’t have any more problems with the bottom bracket for the rest of the ride.
I did decide to replace any adjustable bottom brackets on my older bikes with cartridge versions, but I never did. I still have a few of the old-school bottom brackets in use…just not on any dedicated off-road bikes.