It took my boyfriend and I 31 days to walk from St Jean to Santiago. We only had one rest day, due to blisters) in Logrono. We are very used to long distance trekking, having done the Tour de Mont Blanc, the Corsican High Route, the Swiss Alpine Pass Route, the Pyrenees High Route, the GR 5 in France, the entire traverse of the Cordillera Real, the Cordillera Quimsa Cruz and the Cordillera Apolombamba in Bolivia, several Inca trails in Bolivia, the trek to Macchu Picchu in Peru, etc. With the exception of the Corsican High Route, I can honestly say that I have never been on a trek that has been so hard on the feet. The Corsican High Route is tough on the feet because the first week is essentially on very rocky paths. The
Camino Frances is hard on the feet because it is mostly flat. So, If you walk for 20 to 30 km per day your feet just get the same pounding in the same place hour after hour. At least if you are walking in the hills, your foot is always in a slightly different position and so it isn't such a strain on the tendons. We are well used to walking over 30km a day, but during the Camino we eventually had to settle with 20 to 30 km for most days (though we did 30 to 37 km on most days between Burgos and Leon (it took us 6 days for that stretch)). My two top recommendations are to strip back as much as you can from your backback. We started off with too much stuff (i.e. stuff that we could normally carry into the hills, like a tent and cooking stuff). This got posted back in Logrono. Also, if you ever see something called 'unguento peregrino' buy it! It is essentially vaseline that has been infused with eucaplytus, mint and other nice stuff. It is great for massaging into the feet at the beginning of the day and does prevent chaffing. It is also magic to be able to rub this into your feet at the end of the day. I would also recommend a pair of sandals (not flip flops but something you can walk in if you have to). I find in hot weather that my feet swell a few sizes. I had bought larger than normal walking shoes for this trip, but they weren't big enough. So I developed a few blisters until I bought an even larger pair in Logrono (old ones were posted back). I normally take a size 39 European and the pair that fit in the shop (I bought them immediately after we arrived so that my feet would be at their maximum swolleness) were 42. When we booked our flights, we didn't leave enough time to go onto Finestere, which we regretted. This year, we are doing the Portuguese Route and have factored in enough time for injury days and to go to Finestere and Muxia.
What ended up making it all the way to Santiago? Light weight sleeping bag and foam pad (just in case), walking poles, sandals, walking shoes (you don't need heavy boots as most of the Camino is on good surfaces), two sets of clothing (Camino clothes (lightweight/fast drying shirt and shorts) and evening clothing (fast drying shirt and trousers (washed clothing dries very quickly)), socks and liner socks (bridgedale) (3 pairs), underwear (3 pairs), very light weight fleece, rain jacket, rain trousers (you will be thankful for this when you hit Galicia), sun hat (Tilly), sun glasses and normal glasses, suntan lotion and aftersun lotion, compede (but you can get this at most pharmacies along the way), a needle for pricking blisters, ibuproflen (anti-imflamatory + pain killer), ear plugs (for albergues), watch with altimeter and alarm, anti-histamine pills for insect bits (warning, there are bed bugs on the camino and when you are bitten you will be glad you have anti-histamine tables), zink oxide creme for heat rashes, 2L camelbak water bag, guide book, a small bottle of alcohol (toughens skin on feet and acts as a disinfectant), pilrgrims foot ointment, a datastick with important files from work just in case I had to try to sort something out from an internet cafe, a mobile phone, a head torch (we would start off half an hour to an hour before sunrise), tooth brush, tooth paste, deoderant, a hair brush, bio-degradable soap, camping towel and a camera. Safey pins are also a good idea if you want to hang drying clothing off of your bag. Some people also bring a portable drying line. I have also just remembered (and so used the editing function to add this in) that I had a swiss army knife (scissors, knife and corkscrew all useful) and a foldable Swedish army cup (handy at the fuente de vino and for generally filling up the camelbak).
Buen Camino