Personal head canon after watching "Robot of Sherwood": The Twelfth Doctor occasionally eats ice cream directly out of a carton. Just because he can. (Hey, there has to be some reason he carries a spoon now!)
Direct From the Carton
Clara walked through the hallways of the TARDIS, by now used to the way the path seemed to warp and change at any given moment. Every once in a while the sneaky time machine would dare to play mind tricks on her, but she assumed a good deal of the TARDIS's malice towards her had faded away.
When she walked past one of many kitchens on the long walk back to the console room, she heard noises from inside. She heard the soft pitter-pattering of feet, and the fridge (or the freezer) door closing. Knowing there was only one person besides her on this ship, she peered around the corner. The Doctor sat at a table facing away from her, a spoon and a quart-sized carton of vanilla ice cream in hand. The corner of her lip turned up as she watched him slowly shove a scoop of the ice cream in his mouth.
After a few seconds of watching him eat, Clara found she couldn't watch anymore. This was just... Odd. Did each Doctor have a weird food preference? The last Doctor was obsessed with fish and custard, and now this one ate ice cream from the carton...?
"What are you doing?" she asked, leaned against the wall.
His spoon paused in mid-air. "Getting a snack?" he tried, still staring at the rather large scoop balanced on the utensil in his hand.
"A snack? You're eating ice cream directly out of the carton."
"Shut up, I've seen you eat Nutella out of the jar before."
"With a spoon," Clara further pointed out, gesturing towards it with a teasing grin brightening her face.
The Doctor finally glanced up at her, his brows creased together. She could find that timeless twinkle in his eyes, one of the few constants in his ever-changing life.
"Well, what do you expect me to use?" he said, his (quite endearing) Scottish sounding accent becoming thicker than usual. "A butter knife?"
Now not able to contain her smile, she balled up her hand and pressed it against her mouth. "You look like a seventeen year old girl drowning her sorrows in ice cream after a nasty break up," she mused out loud, close to giggling.
"And you say that like you have personal experience in that area," he shot back, grinned impishly, and then continued to eat from the carton.
Clara felt her cheeks start to burn. She was probably as red as a tomato too, knowing her luck. When the room got eerily quiet in absence of a response, (she would neither confirm nor deny his statement) she decided to expertly change the topic.
"So! Are we going anywhere today?"
The Doctor now had his feet kicked back on the table, and spun his empty spoon around in his hand, looking like the epitome of relaxation. "You tell me. Your choice."
He didn't need to tell her twice.
"Meet you in the console room, then?" she asked, excitement drawn on her face.
He nodded once, and she happily ran off down the hall. He could hear her heels clapping against the metallic floor. The hints of a smirk toying across his lips, the Doctor hopped to his feet and traveled across the kitchen. He placed the carton of ice cream- now at least a quarter empty- back in the freezer. He looked at his warped reflection in the concave side of the spoon, licked a smear of melted ice cream off, and then slid it in the inside pocket of his coat. For all he knew, it might come in handy one day.