Water, that is.
Especially when it gets hot.
There is a booklet for this route too. Also a Spanish site (use Bing translator?)
"The route I chose in 2011 was the Camino Mozarabe or Via de la Plato which runs from Seville to Santiago, around 600 miles (1000kms). The length of time that the journey will take will vary considerably and will depend on your fitness, but it is essential that your planning is thorough. "
Michaal Jones, Coventry.
With an idea of how far you can walk each day you can roughly plan where you expect to stay. Remember as you progress, you automatically build stamina and you may be able to walk further. With this information you can estimate the overall journey time. Add four or five days, to allow you the opportunity to be a tourist for a bit and maybe a rest day or two. company.
Walking from Seville, there were considerably fewer pilgrims than the Camino Frances. Seville is known as the frying pan of Spain so avoid walking in July and August. It took me a while to acclimatise to the heat, but following advice, I drank a litre of water before I started walking each day with regular top ups on the way whenever I had the opportunity. It was also worth carrying an apple or an orange as they held quite a bit of moisture.
A good pair of quality walking shoes or boots is essential, ideally waterproof and comfortable. I favoured a robust walking shoe rather than a boot and with a firm sole; the terrain is rarely smooth, often dusty tracks or rocky paths. Also a new pair of socks with a decent cushioned area; they will be washed daily so will wear out.
Other than one change of clothing, a wide brimmed hat and a waterproof, buy small packets of suncream, after sun, toothpaste and shampoo that can be used for both showering and washing clothes, all in 50ml or below so they can be taken in the plane as carry on luggage. A small torch or head lamp will be useful, ideally LED so you won’t need spare batteries. A micro towel is also useful and will dry very quickly. Also some safety pins, to hang your wet clothes on any available line or fence. Many people favour a stout pole or walking sticks, very helpful when descending steep paths or slippery surfaces, these are best bought in Spain because they can’t go in the cabin of the plane.
Easyjet flies directly to Seville and if you book early, flights for less than £50 are easily achievable, they also fly back from Santiago to Gatwick.
Compostela from the South:
The Via De La Plata
High points include some wonderful historical towns and villages, the Roman amphitheatre and theatre at Merida, the 13th century mediaeval town of Cacares completely contained within the modern city, the walled town of Gallisteo, the four square Roman arch at Caparra (through which you walk) surrounded by remains and foundations of an entire Roman town.
Rural Spain has much poverty, but the people are friendly especially if you try and speak Spanish. You need to get the basics because they don’t speak English.