Try grape picking or similar aggricultural work, but that is hard work for little reward. If your French is good enough you get seasonal work in a bar or restaurant.
Some places will provide food and accommodation in exchange for a few hours voluntary work each day. For example the Château de St-Ferriol sometimes has places for volunteers willing to help with specialist skills such stonemasonary, dry stone walling, working with lime, woodworking, blacksmithing, leaded glass making, engineering, historical research, excavations; and also for less specialised skills like labouring and gardening.
If you are planning a long stay, then you might consider a job as a caretaker or "gardian". People with large houses that they visit only occasionally often employ gardians to keep an eye on the place, often with a grace and favour cottage thrown in. A gardian's life can be a very easy one, but of course it is not always as easy as it sounds. If you want a job as a gardian you will need to be prepared to stay for years, and do at least some work - security checks, maintenence, gardening, forwarding mail, possibly paying bills, heating the place in winter, and preparing the house when the owners are due to visit, etc. To do this sort of job you will need excellent references (catch 22) or be a retired professional. Retired couples are particularly sought after.