The hardness of the surface doesn’t matter as much as what the materials to be adhered are made of. Bare wood is porous for example, so generally you’ll want to use a permanent “white glue,” but other glues will work or you could even paint the wood with a clear liquid sealer or acyrlic paint then use other kinds of glues. White glues dry clear. For cheapness I’d suggest using just plain old Elmer’s GlueAll (you can thin it down with water if you want… try some examples) –not the Elmer’s Washable School Glue– or use a stronger or thicker white glue like Weldbond, Sobo, “tacky” white glues, etc. White glues work well on porous surfaces like wood (if the wood is painted, sand a bit to give some tooth). (“wood glue” is a strong white glue, but it is yellow so could be a problem color-wise.) You can just apply a layer of glue, then sprinkle on the sand and press it all down into the glue, perhaps adding another coat or two of the glue after that all has dried. Or you could mix a bunch
The best type of adhesive to use to glue sand to a hard surface may not be an adhesive. Or more correctly, a different form of a common adhesive. Polyurethane is used as an adhesive, but the form to use for your project would be a polyurethane finish.
Nearly any paint or varnish could work for this application. A common practice for traction control on wooden steps is to paint the surface and spread sand on it while the paint is still wet. This technique provides a slip free surface for many years, usually as long as the paint life.
But we are looking for the best choice. Polyurethane provides a superior finish on nearly any surface. Its surface bonding characteristics are equal to or greater than any paint on the market, with the exception of paints that are specifically formulated to bond with plastics. The gloss available in polyurethane products can be nearly as smooth and shiny as glass.
If you are working on an art project you will want to spread your sand artistically. Other applications leave room for different techniques. Traction control, as stated above, will work best when sand is sprinkled on top of the polyurethane. For other applications, if you want the look and feel of sand and would like an even spread, you may want to mix your sand into a small amount of the polyurethane and paint them on together.
Polyurethane products tend to be rather thick liquids. You may want to have a proper thinner on hand before you begin your project. Ask your paint supplier what he has on hand that is appropriate.