I've been reading various pages about this, and there seems to be many approaches.
Does it make sense to put the RTC also in the 3.3V "realm" along with the microSD ?
So far, it looks like SN74LVC245A is a good way to convert from 5V safely to 3.3V.
I could use this to drive MOSI, SCK, SD_SS, RTC_SS.
On the return, is 3.3V taking chances on not working with 5V or is it generally solid? Connecting the MISO from both devices directly would work if you only activate on at a a time. Or should this be level shifted from 3.3V to 5V to be done properly? What to use?