Well it wasn't on holiday, so I don't know if it counts, but when I lived in Ivybridge, Devon there were a number of good charity shops. My in-laws always liked visiting them whilst staying with us. But as heathfield says you can find charity shops in almost every town, and a fair number of villages.
Oxfam in Wimbledon SW19 has for many years been the highest grossing Oxfam in the country because of the quality and brands of the clothes and items donated, with it being a very affluent area.