Keeping Track

Thankfully nowadays there is now no need to count every seed in a packet for the amount is shown on the back (also gives the price). Not every seed need be sown of course, and many will keep viable for at least 5 years, probably longer if they are kept in the fridge or freezer. But if we know we have 100 seeds, then we know they should grow into 100 plants, and if we can be bothered to sow them all, each edible that is home-grown will save us a heck of a lot of money.
One pack with many seeds can last for years and we can also save seeds from our own plants. Heritage seeds are a good idea as they have far more flavour than the ones the EEC (is it?) that allow to be sold.

Even shop-bought produce can have seeds that can be sown. A fairly ripe red bell pepper, or butternut squash has many seeds and when sown each seed will produce a plant that will bear many fruit (I usually allow four to a plant to allow them to grow to full size). If plants are grown on the windowsill, the flowers are helped to 'set' by pollinating with a small (art-type) paint brush.