I've worked in the photofinishing industry for quite a lot of years, including handling what we'd call "spill procedures." I'm not going to talk from that aspect, just mentioning that I have some experience in this sort of thing.
My opinion is that everyone using photochemicals should have some idea, ahead of time, what they are going to do if something goes wrong. Of course, you can always wing it on the fly when something goes wrong, but once something goes badly for you, you'll probably start planning out the next "event." For example, what do you do if some of that developer splashes in your eye? Or what if my gallon bottle of whatever gets broken? Once you start thinking ahead, you may start keeping an eyewash bottle around, or start storing your chemical bottles in a plastic tub. Or maybe you start keeping a wet/dry shop-vac around (don't even THINK about using it with a flammable liquid, though).
I think the MSDS (material safety data sheets) on various chemicals are probably about the best way to pick up background info on what you're using. I'm from the U.S., and we first had to deal with these as part of government regulations loosely referred to as "Right to Know." They applied to what we call "the workplace," which has a certain definition; minimum number of employees, etc. Part of the law was that all employees who might forseeably be exposed to certain chemicals had to be formally trained in how to read and interpret the MSDS for those chemicals (the companies are required to keep a library of readily-available MSDS). So if you are just a hobbyist, the MSDS were not really intended for you, and if you want to use them, the burden of learning what they mean falls on you. At least in the U.S.
When my company first starting collecting the MSDSs, we found a significant variation in the quality of info. The best seemed to come from reputable manufacturers, such as Kodak, who gave much more complete info, as opposed to some aftermarket suppliers, where many of the items would be listed as "not known," or that sort of thing. Over the years, it seemed that even the "good" MSDS became overly "conservative." I presume it was due to litigation, in the same way that a lawn mower might have labels warning not to stick your fingers or toes underneath while the engine is running. Still, it is hard to find a better starting point than a good MSDS.
Having said all this, for a hobbyist at home, the best thing is probably, for most common darkroom chemicals, to mop or vacuum it up, then rinse it down the drain. But it's up to the user to determine what's ok or not; it all depends on "applicable regulations."