I lived in the town where Pinkpop is held, for a few years, before moving back to the UK in 2016.
I'm not sure about your camping queries, as I lived literally a ten minute walk from the festival entrance, so always slept in my own bed, when I went!
For travel, I guess it depends where you're coming from. You could fly to Eindhoven or Maastricht. You can then get the train from either (probably will need to change in Heerlen, to then get the train to Landgraaf, where the festival is). Another option would be to get the Eurostar to Brussels and get the train from there - I did this a couple of times, going the other way, for festivals in the UK. From what I remember, you'd need to change trains at Liege and either Maastricht or Heerlen ( I forget which).
As for shops, the festival is on an old race course on the edge of a town (Landgraaf), with the campsites dotted about the town. There are 3 (small by UK standards) supermarkets in the town, Albert Heijn, Jumbo and Aldi. So you should be able to get any food and drink you need from there.