We all have left over envelopes, they are cheap and have unlimited uses. Below are are 2 examples of a twist on cards made from envelopes. Great for cash, a pack of tea, small flat candy bars, gift cards, etc. Pick any theme you like from Birthdays to Christmas.
Plain white envelope, opened the flat and stamped on the front of it, I used CTMH inks and matching cardstocks.
Turn the envelope over stamp on 2 corners below the flap, stamp a message if you like. You don't have to stamp all the back because most of it won't show when it's folded.
2 mats of cardstock and a stamped image, added to the front lower side of your flap. Use removable tape so it will open and close freely.
Take any colored envelope you happen to have and use some leftover dimensional embellishments from your stash-- can stamp leaves or stems, draw them on or use bling as I did. Add a ribbon on the top and add a special tag if you like.