A proper place to display your merchandise is something of importance, we all buy with you eyes first, the best tasting food will not sell if the presentation is crap, period. So a proper shelving unit is something worth investing in, brings an attention of a potential buyer and makes the store complete.
I personally love thick, natural boards, but it all depends on the rest of the interior design. Wood though, is a very forgiving material, you can play with it, change colours (most of them) and reassemble it in another way if you wish. Using reclaimed wood is especially wise, since there is an abundance of this type of material in every city.