What is octanamide used for?
Well, one thing is as plastics. Nylon is a linear polyamide; it's traditionally produced from alkyl-diamines and a dicarboxylic acid (to donate the acyl group of the amides, as well as a second alkyl chain joined directly to the carboxyl), and the typical product is a poly-hexanamide, but nylon-8,x variants are also possible, as are reactions involving a more direct route of welding the monomers together and arriving at the same place.

Some Google-fu turns up a number of possible end products for which octanamide aka caprylamide would be a useful intermediate. By itself, it's an emulsifier and common solvent in organic synthesis. Other alkyl amides including derivatives of octanamide, often with a few additional alkyl or amino groups welded on, are used in drugs, inks/dyes, fragrances, and skin care items. N,N-dimethyloctanamide and N,N-diethyloctanamide appear to be common ingredients in deodorants and sunblocks, though I'm not sure if they're an actual fragrance or a carrier/stabilizer (Edit: they seem to be emulsifiers and stabilizers for essential oils of the fragrances in water-based products).