photos by Rachel Pieters cc-by-nc-sa
(a regular envelope will work just fine)
Photo by rpieters cc-by-nc-sa
My favorite way to save tomato seeds is to wash the tomato pulp and seeds in a mesh strainer and then let dry in a single layer on a paper plate or paper towel. After the seeds are completely dry, either gently pry seeds off paper plate or cut paper towel around seeds (seeds can be left on the paper towel, the towel will dissolve when planted).
Another way to save tomato seeds is to ferment them. Here are instructions how to ferment and save tomato seeds from The Spruce
image from https://www.pickpik.com/bell-pepper-sweet-pepper-capsicum-vegetable-vegetarian-nutritious-67436
image from https://www.pickpik.com/zucchini-vegetables-harvest-garden-green-bio-88808#google_vignette
When you are saving seeds from squash, it is a good idea to not only make sure that the vegetable is mature, but let it over-mature to make sure the seeds are large and fully mature (that perfect sized zucchini or eggplant for eating might not be mature enough to save the seeds from).
image by Tiia Monto
image by rpieters cc-by-nc-sa
image by rpieters cc-by-nc-sa
image by Su Yin Khoo
When bok choy bolts- or goes to seed- it sends up a tall stalk and green seed pods start growing on the stalk. Wait until the seed pods are brown. An easy way to collect the seeds is to cut the stalk and to pull the pods and put all the pods in a bowl. take another bowl and gently crack the pods open over the bowl and tiny black seeds will come out.