And here’s Sunday pic! Some relax for all, including the doughboys who come probably back the town of their camp’s PX. Indeed they all wear boxes and tins under their arm…
I just wonder if the term “PX” can be used for WW1 stuff, as I think the term was invented after. Does anyone know more about the origin of this term?
Some WW1 Photographs... 
Post Exchanges (PX Stores) have existed prior to WW1. I can remember reading about them in some early US Army historical books in the old forts in the Wild West. Originally they operated as a kind of in Fort Trading post but today they are more like retail stores. There were other similar things in the British army, “Company Stores” I think and even today, or @ least in the 80’s, there were “On Base Stores” or shops in Australian Army bases where items like shoe polish, metal polish snacks etc etc could be bought.
Ah I’ve just found a site (http://www.fundinguniverse.com/company-histories/army-and-air-force-exchange-service-history/) which states that the term PX was created in 1919, even if Post Exchange system is in use since 1895. Therefore I confirm that the tem PX was unknown during the Great War. In any case many thanks to Sam Point for the comment!