I have never actually tried it, so I don't know if it can be done. With that said, I have never, ever seen it done this way; I would advise against it (unless you are just experimenting) - there's probably a good reason for not doing it (likely noise immunity or power fluctuations in one chip causing the other to reset or something).
Generally you cannot put ICs in series. Putting them in series will force them to take the same current. ICs tend to be complicated and the current that they take will vary. If one IC wants to take more current than the other, there will be a big voltage imbalance.
With a clever regulator circuit, you could run two 3 - 5 V devices from a 9 V supply to save current. However, the design of the regulator circuit, and how much current it would save, depends on what ICs you are running.
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With a clever regulator circuit, you could run two 3 - 5 V devices from a 9 V supply to save current. However, the design of the regulator circuit, and how much current it would save, depends on what ICs you are running.