In general, you need enough supply at the head end so that, after all the drops along the way (including the cumulative current loads of them), the last one still has enough supply.
As mentioned, an LDO on each is probably a good idea, so each unit still gets the 5V (or whatever) it needs, while the supply can be anything higher than that.
If higher current is needed, then switching converters and still higher voltages (12, 24?) are desirable.
If still more power is needed, consider an alternate power network, like fanning out 24V (or 48, or 120, or..) through large cables, which may be routed in parallel with the signal cables, but sooner or later must form loops (i.e., a second power supply chain joins in the middle of a signal chain). Loops in a cable system are bad. The best way to address that is to use receivers/transmitters with high common mode tolerance (RS485 should be pretty tolerant of this already). At higher voltages and currents, you may find the transceivers need to be fully isolated! Keeping such a system quiet for EMC purposes is also a challenge.
If you are using a power fan-out network, be sure to fuse each branch that is not rated to carry the full current capacity of the source. You might use a 24V, 50A supply to energize an LED lighting installation; but each power supply chain might only need 5A, and might be wired with 5-10A rated wire. Each chain therefore must be fused for 10A, so that under fault conditions, it does not accidentally carry the full 50A the source is capable of.
Tim