Double sided tape
This is for use for sticking the various waterproof membranes in place.
3M 9589 Double sided tape. Half inch width is about $10 per 100 foot reel.
Other wider widths are also available (but half inch will be fine).
http://www.uline.com/BL_6028/3M-9589-Double-Sided-Polyethylene-Film-Tape
Another possibility is SIGA Twinet double sided tape available from albert.rooks@mac.com. A 50 yard reel is about $40.