Shelf life of herbicides varies from product to product, but if they are kept in good storage conditions (above freezing, not too hot, dry etc.) they generally last for years. An inquiry to the manufacturer will give specific advice. Fertilizers are generally very stable as long as they are kept dry, tightly sealed, and are not allowed to absorb moisture from the air.

I'll re-emphasize that pesticides of all kinds (herbicides, insecticides, fungicides) can lose their usability if exposed to freezing or very high temperatures or light.