I had lost my Nikon 18-200 mm lens cap. You could spend (at least) 13 euros on a replacement cap (www.fotokonijnenberg.nl/product/6925/nikon-lc-72-72mm-sna...), or you just buy a Nutella chocolate spread. You not only will have a drinking glass in the end, but also a lens cap !
You need the Nutella 220 grams jars specifically (www.google.be/search?hl=nl&safe=off&q=nutella+spr...)
Also, it works great to set a custom white balance: just leave the cap on, set the white balance, remove the cap, and all done!