What do you do with Unwritten Postcard in Envelopes?

I know and those minisheets can be really nice. I recently bought 2 gibraltar ones, mostly because cards from there are harder to get but I wouldn’t swap for them. I don’t have limited funds to swap so I just swap for what I like most, the complete package. When someone wants to swap and prefers multiple blanks in an envelope I offer to send blank cards in envelope for less cards written and stamped to make it a fair trade.

i don’t like so much unwritten postcard in envelope, i don’t consider them as a part of my collection.
i usually like to send to myself a postcard almost every week: they could be postcards i bought weeks/months earlier or unwritten postcards in envelope i received, so they become part of my collection.
if it’s a landscape sometime i cut the stamp from the envelope and i stick/glue it to the postcard with the sender’s note and my address, so it become almost a travelling postcard that i can allow into my collection.
if i don’t like those unwritten postcards in envelope, i keep them to send them for somebody who could like them, or i put them into a lottery

I stick them all into my postcard album-blank or written. I write a little caption with the sender’s name, location sent from and if they were part of a direct swap, postcrossing, or a tag. I also add a little note about any cool features about the postcard like pretty stamps, stickers or something interesting mentioned in the message. If the envelope has artwork on it, I will usually keep it. Or at the very least, keep the stamps and place them beside the postcard that I received.

I don’t mind blank postcards in my collection. Before postcrossing I always collected blanks from various trips- especially from museums. A lot of places will not let you take a picture of certain works of art so postcards were the best way for me to get a photo for my scrapbooks.