Environmental challenges such as soil salinity and drought are serious threats to global food security and biodiversity, making the selection or development of stress-tolerant genotypes of crops and native plants necessary. Certain biochemical compounds synthesized by plants are directly involved in ameliorating the effects of environmental stress in characteristic ways. Further, the biochemical composition of edible parts of crops is directly related to human health, deficiencies of certain nutrients being associated with major health conditions and healthcare costs, and public awareness of functional foods also increasing. Interestingly, the unique biochemical properties of some biomolecules involved in plant stress tolerance are also associated with significant roles in human metabolism and health. This work summarises the biochemical properties and functions of four selected biomolecules with such dual significance, i.e., abscisic acid (a key hormone with roles in plant development and abiotic stress response), glycine betaine (a quaternary ammonium compound which functions as an osmoprotectant), vitamin E components (antioxidants), and phenolic compounds (antioxidants), all four also having significant nutraceutical effects.