Mixxing 5v./3.3 v. quandary

I know hat some chips can be destroyed if a substantial voltage arrives on their I/O pins before the chip is brought up to full power on the Vin pin. So now I am slowly using up an inventory of 5 v. Nanos and ProMinis, and almost every new device I incorporate into a circuit is 3.3 v. Now, depending on how I design the power supply, I worry that a 5 v. chip might reach full power and put a voltage on a 3.3v part that is still coming up to power. Or vice-versa.

Does anyone have any rules of thumb that assure this won't happen, or is it just that during power up, the discrepancy would be too short-lived to cause any problem?

Thanks in advance for any insights.

Put series resistors on the control signals to limit current flow to 1mA, the input clamp diodes should keep the 3.3V devices safe.

The 5V on a 3.3V part is an issue anyway, not just at power up. Never route a 5V signal to a 3.3V only part.

Since the 3.3V rail is normally derived from the 5V rail you don't have to worry about phantom powering usually (unless connecting two boards each with its own power).