In the good old days part of my toolkit was a nail and a suitable size nut. A roadside stone was used as a hammer to push the pin out. I did use it successfully when it was needed on a 1/8th inch chain.
Horrors that would have been 70 years ago.
I've split chains with a nail and and a nut too on plenty of occasions, although never at the roadside. It's how my Dad taught me. I didn't know a chain splitter was a thing until I started reading forums like this! I have also used the nut and nail method on much bigger chains on balers, potato harvesters, etc.
In a photographic book showing the photos of Robert Chapman, who was a prolific Irish photographer and also a keen cyclist c1910, there is a serious of photos of him and the people he was riding with stripping a singlespeed freewheel and doing something to correct a problem with the pawls with rocks and whatever tools they could improvise in the snow, somewhere very remote in the Wicklow mountains. Today, he would just phone for someone to pick him up!