I'd note down the main ones you see for the different areas, or ones linked to the nearest area of controlled airspace to which you will fly. If you have the appropriate French charts, they will be fairly clear to see.
In my experience of VFR in Class E, you will simply get handed over from one to the other seamlessly - more so than you typically would experience in the UK where you have to make a freecall to whoever you want next. In most cases the frequency will be one you have noted down beforehand, other times maybe it isn't, but just write it down and put it in the radio.