IF you plan on doing this long term, you need to do it right. There are some seeds that store well if properly prepared at harvest time, packaged properly and stored correctly.
There are some vegetables that don't store well over time. I've had problems over the years with some types of lettuce and a few other varieties.
I've had some seeds that I've saved that when packed right and stored right that have been viable up to 5 -8 years after stored. The germination rate wasn't the best, but I got enough to grow that I saved the seeds from them to build up stocks again. I've also had a few times I've used seed specially stored in a freezer for over 10 years that germinated and grew well in a test I did a few years back.
I still have a few seed lines for open pollinated varieties that the I got from my grandmother/grand father 30 years ago (they'd been using them for who knows how long before that) that I'm still using.
NOT the same seeds, but seeds that were planted every couple of years and then properly prepared and stored for a few more years, before pulling them out and cycling through again.
The book I started with was the first addition of Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners, which I think is out of print. You might be able to find one used somewhere.
I've used seed saver exchange several times during the years to get something I was looking for that I couldn't find anywhere else and they have some basic information on seed saving-
Seed Saver Exchange
How to Save Seeds
Learn the basics of how to save seeds from your garden. Saving seeds has many benefits and with a few tips and an understanding of what to grow, how to plant, and how to collect seeds, you'll be on your way to seed saving in no time.
www.seedsavers.org
… their a good source for several things, but they are currently closed to any new orders
Here's another basic overview with an estimated time of storage
How Long Do Seeds Last? (Plus a Cheat Sheet on Seed Life)
To the newbies to gathering and saving your own seeds, you have to start with
Open Pollinated varieties,
hybrids (even F1's) don't breed true and the seed from them isn't worth trying to save or use.