One of my favorite things to do when the weather is cooperative, is to go outside and see what kind of medicinal and edible plants are in my area, and gather up some for drying or using right away.
There is a lot of Mullein in my area right now, which I have found useful to make tea with and it helps a lot when I’m having respiratory problems. The spring season is really a great time for foraging in my area, but all year round useful plants can be found.
Don’t be discouraged if you live in a city, if you look, I bet you can at the very least find plantain and dandelions. Buy a book or two for identifying plants in your area, if you can’t buy one, go to your public library and borrow one and take notes. Be sure not to gather more plants than you can store, no sense in being wasteful.
Here are two sites that I found useful for reference, though I prefer books that I can carry with me outdoors.