These are the zoology field guides that travel with us:
Les Papillons de jour de France, Belgique et Luxembourg et leur chenilles, Tristan Lafranchis, one of the outstanding Parthenope Collection of field guides for FBL, published by Biotope, 2000. Distribution maps (indicating status by départment);good photographs of adults in the field, illustrations of caterpillars not so successful, mais c'est déjà ça; good notes on plant associations, habitat and flight periods.
Field Guide to the Dragonflies of Britain and Europe, by the Dutch expert KD Dijkstra and illustrated by the incomparable Richard Lewington, British Wildlife Publishing, 2006. Lewington's beautiful illustrations allow all diagnostic features to be clearly indicated. Distribution maps (small, as they show the whole of Europe, but borders and major rivers marked); notes on habitat and flight periods. Limited to adult dragonflies and damselflies, so if you are into pond dipping and have netted a fearsome nymph or want to identify an exuvia, this book cannot help you. Also available in French.
Guide des Mouches et des moustiques, J & H Haupt, Delachaux et Neistlé. Originally in German, this provides a good overview of the diptera (true flies) of Europe, with an interesting (not dichotomous) key to families in the front. The photographs are often not very good, and a beginner would be very unlikely to get an accurate identification from the necessarily small selection of species featured, but for a more experienced amateur, it provides a useful aide memoire. Diptera are so numerous and so diverse, that no one is an expert in all families, so it can be helpful to have this little book to remind you what the possibilities are. The descriptions and ecological information is brief but useful.
Insects of Britain and Western Europe, Michael Chinery, Domino Field Guide, revised 2007 edition. A general guide that will give you an idea, but quite often not an accurate identification. The choices of species included are sometimes curious, in that they are not always the most likely to be encountered. However, it does provide an excellent overview of the possibilities (even if there are too many moths and not enough flies). It has a 'twin', Insects of Britain and Northern Europe, by the same author, and they are frequently confused. IoBNE is favoured by many professionals as the better book because it has keys, but it is let down by its inferior illustrations and by the fact that it contains fewer species that are relevant to France and Britain. I have packed IoBWE for its general usefulness, and because it is quite good on bumblebees, a group for which I don't have any literature that covers France (although I have several excellent guides for Britain). Hymenoptera (bees, wasps and ants) in general are not well served by field guides.
Field Guide to the Mammals of Britain and Europe, F H van den Brink, Collins, 1967. We picked this up for £1 when our local library had a chuck out session. An oldie but a goodie. Distribution maps, good colour illustrations of each animal, lots of black and white drawings of tracks and signs. Of course, some of the scientific names are out of date now.
The European Families of the Diptera: identification, diagnosis, biology; Pjotr Oosterbroek, KNNV Publishing. Originally in Dutch. Not strictly necessary to travel with, but jolly handy if I get anything I can't immediately slot into a family. Beautiful line drawings.
Les Libellules de France, Belgique et Luxembourg, D Grand and P Boudet, Parthenope Collection by Biotope, 2006. (One I don't actually have yet, but Summerfields Books will be receiving an order shortly.)