My Isekai Life: I Gained a Second Character Class and Became the Strongest Sage in the World! manga volume 21 features story by Shinkoshoto with art by Huuka Kazabana and Ponjea.

Yuji Sano was a normal guy working a soul-sucking nine-to-five job when he suddenly found himself transported to a fantasy world where he restarted his life as a Monster Tamer. After befriending the Slimes, Yuji is quickly able to gain a second character class, ranking up his stats and learning new skills as he encounters one surprise after another.

While enrolled at the Royal Academy, Yuji finds himself forced to participate in a school field trip from hell. After lugging a sixty-six-pound backpack around for half a day, he comes to the horrifying realization that all they have for dinner is...rocks and grass?! Faced with the prospect of slowly starving to death, Yuji realizes that he'll have to work with his classmates if they're to survive this diabolical walk through the woods!