Since I am just starting out on this journey I obviously just hunt for excuses to give my cakes away. I made a bachelorette party cake for a friend of mine (for a party she was throwing) but had no way of transporting it except on the bottom of one of those little cake containers, and I "glued" it with bc to minimize movement. I gave it to her 9 days ago and made her very well aware that I needed the bottom piece back asap. I have not heard one word from her. She has not even written or called to let me know how the cake went over. I have decided that's the last time I'll do a cake for her, and in the future, if a cake leaves my posession, it's not with anything I'll need back. That is the only thing I had that was suitable for transporting cakes and I'm not driving 40 miles roundtrip to get it from her. I will go out and purchase something else because I need something for my valentines cakes and she will not get a cake from me again. It's free for goodness sake, show some more gratitude. I'm irritated but I guess it's a lesson learned.
I know how you feel. I have taken cakes to people with the heavy boards underneath and explicity told them to please return them. I cannot tell you how many times they have come back and said they threw it away. GRRR!! Those boards are expensive. Now I just add in the cost and tell them if I get the board back, they get the money back.
Cindy
I would contact her & tell her you need that back or if she'd rather she can put you a check in the mail for x- amount. I had this lesson also. My ex-SIL caleed & I did my nieces 16th b-day cake. I loaned her my best cake platter. This was October 06. Still no platter or anything. What the heck are people thinking.The cake was free. 
I'll have to take the loss & next time I will charge her, add in for the cake plate.
As a side-note:
I used to use that same cake carrier you have in your pics! Let me tell you ... I took cake over for dinner and there was a ton left over. I left the whole thing there. Nearly TWO WEEKS later they said they had JUST thrown the left overs away but that they had been slicing away at it day by day (only 2 of them in the house) and it was still soft and fresh-tasting as it was on day 1. And it was sitting out on the counter. Is that crazy or what???
That creeped me out a little and I immediately started to buy cardboard cake pads and bakery boxes. I don't want any of my friends eating 2-week old cake unless they have purposly wrapped or froze it themselves.
I hated learning this lesson! I learned a long time ago to charge a refundable deposit in the amount of the cake stands/carriers that I give them!
I write on the underside, in black magic marker, "Return to Cater It Simple, (phone #)". That way there is no question on whether it gets returned or not.
One of my catering brides asked me to cut her cake that she had gotten from a local bakery. They have special stands made (that made me want to just SCREAM since there was no freakin' way to tear the cake down! aaauuuggghhhhh!!!!!!!!!!!! 
) and imprinted right on the plastic plates and stands are the words "Return to XYZ Bakery".
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