@pixel , I walked the Primitivo in July last year. I spent the grand sum total of 200 Euros in cash in those two weeks. I stayed in a mixture of accommodation : a simple hotel in Grado, the wonderful Bodenaya, the new Albergue Pascual, and a mixture of other Albergues along the way. Bodenaya & Pascual are donativos, so naturally cash. I think with the exception of the Xunta that I stayed in, everything else I paid with debit card. Cash may well be appreciated by some of the smaller family places, but it is no longer 'King' on camino.
I visited a good number of cafes. A few places had a minimum spend of 10 Euros. It can be high as 30 euros, however I only once came across that. Anything over 30 euros
by law the business owner has to provide for alternative means of payment - however that can be something as crazy as a bank transfer, not really viable for you and I on Camino.
All of the supermarkets I shopped in happily accepted my card.
I questioned a very friendly cafe owner along the route, he actually said that he
prefers card because it makes life a lot simpler for him at the end of the day. Minimises costs and paperwork; and minimal banking to do! (He does not pay his suppliers in cash).
A moderate proportion of the 200 euros cash I gave to other pilgrims for my share of a cafe or dinner bill so they could pay with card. Saved them having to go to an ATM for cash.
Bed bugs - zero issues. Frankly I'd be more concerned about them when visiting Paris! It's like everything:if it happens, it happens - but it's not particularly likely.
Whilst you haven't asked (as it's come up above) if I may be so bold my personal guide to my donativo is simply: pay what you can afford.
For me that means:
1)What I would pay for my nights accommodation elsewhere.(€10+)
2) what would I pay for my dinner and /or breakfast elsewhere. (Eg both: €20)
3) leave a little something extra for the next person who may be in need.
What you pay affects what tomorrows Pilgrim eats.