I use nappy packages inside out and keep anything I get sent.
I usually get a medium pack of parcel bags from the pound shop. They’re a fair size to fit baby/toddler clothes in or even footwear. You only get 3 in the pack though.
Buy a pack of parcel bags from amazon. Think you get 50 in a pack and they're all different sizes. Well worth it if you've got a few things to sell. 😊
I just bought parcel bags from Amazon
I usually keep bags/envelopes that I get sent and reused them. In my experience most people tend to do that.