Okay so personal headcanon that Oga didn’t pack any shit for this trip and is now just mooching off of Furuichi’s suitcase.
No, he doesn’t see the problem of best friends sharing underwear either. As long as he gets to wear them first of course.
It probably doesn’t help that Furuichi is being the most inattentive best friend ever! He totally deserves to get his clothes stolen.