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I suggest picking up a few picks every time you go into a musical instrument shop. They do not cost much and you can keep a lot of them in a small tin or box that will fit in most cases. Each pick will deliver a new sound without changing strings, but you need to be aware of the risk of gouging or scratching the wood.
If you are interested, you can make your own picks. There is a tool called a pick punch that punches out pick shapes. You can recycle various plastics by using the tool or just cutting out the shape with sharp scissors or a craft knife. The plastic used for milk bottles in Australia works well. If you are a woody you can shape some scrap into a pick.
You can also glue some felt to both sides of a small sheet of plastic and chop out felt picks. Ice cream container lids are a favourite material for this.
I tend to buy them because I can go to a shop. But if there was no shop I would just chop up plastic containers and make some.
One of my favourite picks is the little tag used in Australia to close the plastic bag holding bread. It makes a really bright tone. They are just under 1" square.
Yes I know about that device. Ok for guitar picks I suppose, but I have plenty of guitar picks already. I wanted to try felt and leather picks, and I'm glad I did!