If you are like most gardeners, you probably have tons of seeds from last year (and from years before!). Since different varieties have different “shelf lives”, you may want to do a quick germination test before you toss and reorder.
Wet a paper towel (moistened thoroughly but not sopping) and place 10 seeds on the top half. Fold the bottom over the top to cover the seeds and seal in a zip-lock baggy. Blow a little air into the bag so the seeds have a bit of oxygen, then put the bags in a dark place where you won’t forget to check them (I chose a kitchen cabinet).
Wait about a week (different varieties have different germination times — check the seed packet), peel off the top paper towel and count how many seeds have germinated. Fewer than 50% and you will probably want to re-order, 50% to 70% you would plant more thickly than usual, and over 70% and the seeds are as good as new!