Items that could be printed out individually to put on the outside of envelopes or put on cards. Like wax seals that say thank you, or your invited, or congrats, or have a graduation cap, or birthday balloons or candles. In lots of different colors but not just primary colors. Washi tapes that say thank you, happy birthday, thinking of you in different colors (not just primary colors) and black and white that could be put on the back of an envelope. Anything that could be glued to the outside of an envelope to make it more exciting than just a plain envelope.