Cassian had his doubts about Jyn truly wanting to 'fit in' anywhere prior to her recovery by Rebel forces on Wobani. But that was then and this was now. Neither of them had a reason to stay on the outside now it seemed.
He didn't bother to hide the smile at the sight of K2 wearing something so garish, and he looked around to find a pair of pants that looked like it might fit his friend. "Try these."
For now he'd focus on the practical matters of clothing and food, and let Jyn and Kay-tu banter.