Glues for Collage

  There are dozens, maybe hundreds of adhesives available to use. 

 One good basic glue mix is 1 part white glue plus 1 part acrylic matte medium, applied with a brush

Heavy cardstock works, as do other heavy papers. 140# to 300# watercolor paper is great for special work.  Cardboard is stiff enough but has so much acid in it that it's not recommended for work you want to give or sell.