if you have a wife that does alot of sewing, old used up thread reels work as good spacers, 1x1's mounted to the wall work well also. You can get a pvc pipe 1/4 inch and cut sections to use as spacers, you can also use gutter ferrels cut in half as spacers.
Keep in mind, the smaller the spacer the more of the holes you can use for storage. 1x1's work good but take up many holes. But if storing long handled earth tools, maybe you need the support of 1x1's to handle the weight.