A lot of vegetables can be pickled in vinegar and made usable for a long time. Canning also preserves foods. Other methods may include salting, drying or smoking. With these methods, food does not need to be transported and sold immediately. Juicing is an option as is freezing foods whole or while in juice form, if freezing is available. These ideas are easy to research and many details depend on where the farm is located and what is available for resources. I wonder if in some areas there might be electricity in town and freezers or juicers could be rented out to farmers.
New products could be created such as condiments and dressings. With proper marketing specialty jarred products could be created. Chutney's, relishes, sauces and pickles can all be preserved in jars and or cans and increase shelf life. It has to be done under the correct conditions or the food can become a deadly poison.
Some times it seems as if change requires more man/women power, possibly farmers could hire help and pay wages partially with food.