I keep seeing these ads come up to buy your own survival seed bank, just in case of emergencies. While it's a great idea, I don't fancy buying tiny paper packages of fancy seeds wrapped in mylar for $150 bucks.
Buying and storing seeds is not hard and doesn't have to be expensive. The only real 'trick' to this is to buy open-pollinated seeds.
Your other choices are hybrid seed types (cross pollinated between two types of plant, making a pretty, new variety but one that won't come back true to seed in the same form, year after year) Another small piece of advice is to only buy seed that will grow well in your area. Where I live that would be kale crops such as spinach and cabbages, broccoli, onions, plants that don't mind the cold.
I save seeds yearly and this year, intend to go to the hardware store and buy myself a piece of pvc tubing, some plumbers cement and a couple of threaded end caps. Cement one end shut, store the seeds in plastic vacuum sealed packages and tuck away for future use. Seeds stored in a cool, dry location in this manner will last for many years. Just in case!