A Value packet is not waste if you keep the remainder properly, and keeping it properly costs nothing.
Cool, dark and dry, in that order. A sealed tub in an unheated room beats a drawer in a warm kitchen, and anything that has been damp once is finished. Write the year on the packet the day you open it.
Rough viability, stored well: tomato, cucumber, lettuce, chard and beetroot stay good for four or five years. Broccoli, cabbage, turnip and spinach give three or four. Peas and carrots drop away after two or three.
If you are unsure, test before you commit a bed to it: ten seeds on damp kitchen paper in a sealed bag somewhere warm. If seven come up, sow as normal. If three do, sow thickly. If none do, you have saved yourself a month of waiting for nothing.