Insulation
Glass wool batts, XPS and EPS boards, foil laminate and acoustic wool — the volumetric leftovers most jobs don't bother returning.
Insulation surplus covers batts, boards, foil laminates, acoustic wool, and pipe lagging. Insulation is bulky and cheap by volume — anything above a couple of full bags either goes to the tip or gets listed.
Common items: R2.5 and R3.5 glass wool batts (Bradford, Fletcher, Knauf, CSR), R2.7 acoustic wall batts, extruded polystyrene (XPS) boards in 25mm and 50mm, expanded polystyrene (EPS) waffle pods, foil-faced building blanket, reflective foil roll for roof cavities, and closed-cell pipe lagging in various diameters.
Prices are low per unit but the volume adds up. A full pallet of batts saves hundreds compared to Bunnings.
Check batts are dry and not compressed — insulation that's been left damp loses R-value permanently. Look for original packaging (unopened bags), and check thickness matches your framing depth. R-values are only rated when the insulation is installed at nominal thickness, not compressed to fit a shallower cavity.