I just thought I would report how I got the Crawdad Box since I think it was kind of weird.
First time I was fishing for Mr. Pinchy and when I finally caught him, he took up my last bag slot. I didn't notice. I then activated him and triggered the cooldown and got the "Inventory is Full" message across my screen. I was pretty upset because I thought I could have missed my chance at the Magical Crawdad Box and would have to wait 2 days to to ask another wish. Later on I check my mailbox and I received a the following letter with the Crawdad Box attached.
"So, Mr. Pinchy grants you a gift and you throw it away like garbage, eh? Well, you HAVE to take it! But don't think Mr. Pinchy didn't notice. Mr. Pinchy will have his revenge! When you least expect it..."
I was pretty happy. First Mr. Pinchy, First wish.
I looked for any other reference for something similar happening to another person on this forum and the closest I could find was this: http://www.elsanglin.com/forums/topic/that-rat-got-away#post-3638
where several users reported they lost Crawdad Box when the same thing happened to them. I don't know if they changed the mechanic or what not but I was able to get him sent to me.