Not On My Board

I am not an AAC or PECS user and I don't know anyone who uses these communication methods, but   I have seen a common problem with these means of communication. How would one say "What I want to say isn't on my board/included in these card choices?" when they don't have an option to say that? To illustrate these frustrations, I will use hypothetical examples.

Person A uses the PECS system and wants grapes as a reward for doing well in school. Person A's parent offers Person A an apple card, a milk card, and a chips card. However, there is no grapes card in sight. Unable to say "More choices, please" or "I'll tell you what I need," Person A has a meltdown and doesn't get the grapes.

Person B is an AAC user and verbally gifted, but no one knows that because Person B only has basic words on their device. Person B can think "The marching band converges into formations while they play music", but can only say "Walk, music, shapes". This inability to express complex thoughts leaves Person B at the mercy of teachers who say Person B has "no human dignity" or "can't understand anything".

If you are familiar with AAC or PECS, tell me what you do to deal with this problem. Do you have a card that allows someone to say this? If not, I created one. Feel free to grab and print the image.