They have all sorts of stuff - I guess depending on where the store is will influence the type of stuff they have - things like bottles, bottle tops, scrap plastic, paper, card mount board (these cut out shapes are so useful) fabric etc - anything local businesses would normally throw away as faulty, excess or prototype, or stock from businesses that have closed down and would be sent to landfill - if children/schools can use it - it goes to scrap store.
Our store has sort of three sections -
a) the 'scrap' section where you can help yourself to the above kind of stuff - filling a bag and giving a donation as suggested by the staff
b) a section where they keep 'good scrap' and sell pieces individually for a reasonable price - in this section yesterday they had children's plastic shoes, party products and some lovely small wedding ornaments - which I guess are stock from a closed business but not considered 'scrap'
c) a section where they sell 'proper/new' art materials - like acrylic paint, crayons etc at very reduced prices.
One rule is that you cannot get items from the store and sell them on directly. So for example I could not collect lots of yoghurt pots - with faulty printing - fill them and sell them on. I can get the yoghurt pots and use them for mixing dye at home etc.
I joined our store when my children were little so was included in the 'working with children/family' membership - now I am in the 'artist - teaching adult workshops' category. The type of stuff I buy from the store is used in samples, for workshops or the art work I make. If after I have used/worked with it and someone buys a piece from me then I feel justified to sell. I do give more to the scrapstore than the donation requested.
So if you live in UK - the national directory is HERE
Wiltshire contact page is HERE