If you have cracks, small holes, or even the occasional missing piece of cork that need filling, you can make your own wood filler at a fraction of the price.
Mix 2 parts sawdust (collected when sanding the floor with 80 grit paper), 1 part PVA glue and add enough cold water (a few drops at a time) until you get a thick consistency.
Below, I had a few pieces of cork missing on my floorboard but did not want to pay £6 for 18 strips since I would have only used less than a quarter of one.
So, I filled the missing holes with my home-made wood filler.
The neater your work, the less sanding you will need to do afterwards. Then, all you have to do is varnish the floor.
It is all about tricking the eye.