Recall at the beginning of "I Remember You", the Ice King went to his "past room"? There were a lot of interesting items there, such as the Highway 101 sign, and his scrapbook; but one thing stood out: an "EAT" sign, similar to the the one we saw outside the ruined diner in "Memory of Memory".
At first glance, this seems odd and a little creepy, right? The Ice King following Marceline, going after and keeping items that are in some way connected to her. But there's another thing. Recall at the end of "Daddy's Little Monster", what Hunson Abadeer said? "They weren't even very good. They were really cold." What if the fries were Simon Petrikov's last gift to Marceline? Before he left due to the crown-induced insanity, he saved food for her so she can live without him, and that is why the fries were abnormally cold? Just food for thought. What do you think?