With long journeys and particularly during winter I have noticed that the salt erodes the chain very quickly, even when I have lubricated the chain beforehand. When you are missing proper chain lubricants, what would you use as a substitute? Could you use cooking oil if you are missing the right stuff, or should I keep a small bottle of oil with me on my rides?
The best bicycle chain lubricants are sold in a spray can and are thixotropic.
When sprayed on the chain, the spraying action agitates the fluid and it becomes thin as a result of the agitation. The now-thin fluid penetrates easily to the innards of the chain.
Then, when you leave the bicycle to sit, over time, the chain lubricant becomes thick. This causes it to stay inside the chain and not drip on the floor.
When you start to ride the bike, the motion of the chain agitates the lubricant again and it becomes thinner so that it does not resist the motion of the chain too much.
When you park the bike again, over time, the chain lubricant becomes thick to prevent it from dripping.
To test whether a particular spray lubricant is thixotropic, spray it into a small glass container and see how thin it is. It should be reasonably thin immediately after spraying.
Leave it settle for a day. See how thin or thick it is now. If it is thixotropic, it should be markedly thicker than immediately after spraying.
These thixotropic lubricants last a long time. Unfortunately, bicycles are a low-tech application where nearly anything can lubricate a chain in an acceptable manner, so you won't find these thixotropic lubricants marketed as a bicycle chain lubricant. To have the largest chance of finding a thixotropic lubricant, you should purchase motorcycle chain lubricant. Being marketed for motorcycles, the spray can is large, so large that you cannot reasonably carry it with you. Because it is delivered by spray (in order to agitate it during delivery), it is impossible to move some of it to a smaller spray container.
I suspect most sub-500km rides don't need additional lubrication if not riding in the rain. Just lubricate the chain before a long trip. If riding in the rain, the rainwater quickly displaces whatever lubricant there is in the chain and then the chain will be lubricated by rainwater. It is an acceptable lubricant in this low-tech application, but it will evaporate quickly. When the rain stops, the lubrication stops and the chain starts to squeak.
To fix the squeak, there are two options. Firstly, carry a very small drip bottle of any oil with you (doesn't need to be thixotropic as this is an emergency lubricant only). Secondly, if you prefer not to carry the lubricant or forgot it home, try to find a discarded motor oil container from a gas station. Most likely, there will be a very small amount of oil in there that is enough to lubricate the chain.
Don't use cooking oil; prefer motor oil instead as an emergency lubricant.
Oh, and as a reminder, these thixotropic lubricants in a spray can must not ever reach the rear disc brake if your bike has disc brakes. Be careful when applying or use a large object to prevent possible spray to the disc brakes.