I take a small tray that doubles as a cutting board and a knife with a cover, then take washed cucumber, carrots, pepper (also seeded), etc etc and chop and dish out as we drive (obviously I am not the driver at this point!). Likwise fruit - deseeded melon, pre-cored apples and pears etc although oranges can be messy.
If it's hot, melon and cucumber work well to help keep hydrated without lots of actual juice sloshing around.
I also take a packet of cheap White plastic disposable beakers (you can get a huge pack for a pound in the supermarket, you know the sort of thing that you get weak squash or lukewarm tea in at the school fete). I use them rather than plates if I'm handing snacks back to the dc to eat in the back of the car. Much easier for them to hold and less likely to get spilt. Then top up with food as required. I tend to cut things like sandwiches into soldiers rather than squares so they fit into the cups well, the kids love it as it's a silly thing to do (they're currently 8&5 - only happens on long journeys usually on holiday, so good associations) and then at the end I can just throw the cups away so no worrying about washing things clean. Not very environmentally friendly but it doesn't happen very often and you don't actually use that many.
Twiglets are good too.
I also make sure I have a teatowel with me (mostly used as a cloth across my lap to protect it), some kitchen roll and some water (topped up with tap water as necessary) so that I can dampen kitchen roll to wipe the knife clean (cover invaluable to keep it safe when not using, they have them in tk maxx for a couple of pounds usually). And also good for wiping grubby mouths and sticky fingers.
Also make sure I have a pack of smarties/minstrels/fruit pastilles/gums/etc that are exclusively used for playing 'how long can you make this sweetie last in your mouth?' game - essential for a few moments of peace amd quiet
. Luckily the dc haven't cottoned on to this yet and still try to make it last as long as possible, they're happy with the sweetie and I'm happy with the peace, a win:win game!
(and if you don't want to use throwaway cups, the cheap beakers from ikea work well too with the added bonus that the plastic lids from Pringles tubes work as lids - well they did on the old ones, haven't tried them on the ones that have been around for the last few months).
Sorry this is a bit disjointed I've been doing it on the phone with lots of interruptions.
Have a lovely time in France!!