Suggest you make a note of the consumption of various items - water heater, fridge, heater (on lower settings, kettle etc. on a card
Check with the site when checking in and then work out which loads you can have on together. For example, water heater and kettle together usually a no-no on 6 amps. The problem is that many sites do not have their circuit breakers accessable to the visitor and should you trip them by connecting too much load, you will have to go and find the owner or warden to re-set. This is pretty tedious if it happens too often, particularly at night.
Note too that you may be lulled into a false sense of security when first plugging in a new load, say the kettle. If the water heater has been on for a while and has heated the contents fully, then the termostat will operate and it will be taking no current until the water temperature drops again, either when you use some or by natural cooling. This extra load may be enough to trip the circuit which had been working perfectly well beforehand.
There is quite a lot on this topic in earlier postings both in the overseas touring section and in technical. However, as a rough guide, look at each appliance you have e.g. kettle and find the power rating in watts or KW (thousand watts). Assume the site voltage in France will be 220. Then the current taken by the appliance will be given by the value of the watts divided by 220. For a 1000watt (I kw) appliance, the current will be 4.54 amps. You can find the rating for fridge, water heater, space heater etc. from the handbooks for these items, and things like hair driers will be marked on the appliance. Add up what you have or want to connect and keep this below 6 amps to avoid tripping.
Hope this helps - enjoy your holiday.