I haven't walked the camino yet, (will be in summer 2014) but I have lived in Europe for 6 years this round (lived in Britain in the early 90s too) and I can echo the need for small bills/Euro coins,4-digit PINs, and cash.
When traveling outside of the Euro zone, I write up a mini index card as a cheat-sheet for conversions. If I am in Hungary, for example, I have one side of the card listing 1,2,5,7,10,12,15,20,25 Euros (my currency) and what that converts to in Forints. The flip side of the card has Forint to Euro conversions. One glance at my little pocket card and I know roughly what my dinner is costing me.
For those using the Euro for the first time I recommend doing the same with your own currency.
And, for the sweet love of God, please don't try to use US dollars in Europe! My adopted city gets a lot of US visitors and it's amazing how many think they can use their money in another country. Imagine a Japanese person walking into a 7-11 in Texas and being upset the store won't accept his yen lol!!
When I was making frequent trips to Europe before moving here, I always wore a money belt. Mine is a thin cotton one. Since I run hot at the best of times, I can get a soggy passport even on normal plane/train travel. The best thing for sweaty-money syndrome is keeping everything sealed in a ziplock inside the money belt.
Also, I keep the belt contents at the small of my back. I don't have the flattest of tummies and it can be obvious under clothes when worn in front.
I NEVER go into it during the day: money from an ATM goes in my bag or pocket until the nearest toilet. I only look at my cash/cards inside a toilet stall or in a private room at night. Cash for that day only goes into a wallet/coin purse in a deep, ideally zippered pocket.
I have seen tourists pulling out their money belts on the street, at ATMs, at restaurant tables. Stupid. Why wear one, if it's being used as a wallet? Then use a normal wallet and at least seem local.
I don't have camino experience yet, but I do have plenty of travel experience.
I've been traveling alone (female) since my late teens, in the 80s, and I prefer to be efficient, relaxed and confident than marked as an easy prey.