Chapter eighty-eight’s title image is from “Sekai ga Owarumadewa…” by WANDS.
Chapter eighty-nine’s is from “Send To You” by luv.
Page 52 seventh panel, “pohyb” is “movement” in Czech, which is one of the meanings of 運動, but 训练 is the Chinese equivalent of 訓練. (Where’s the Urdu, though?)
Page 53 third panel, I don’t think Japanese can be entrusted with polysyllabic foreign words like “hierarchy”…
Same page final panel, Bocchi’s referencing basketball manga Slam Dunk. (Fun fact, Sekai ga Owarumadewa was the anime’s second ending theme.)
Page 54 fourth panel, 幻の6人目 is a title given to Kuroko Tetsuya, protagonist of basketball manga 黒子のバスケ. Kita possibly thinks she’s referring to Marvel’s X-Men, but perhaps not. (Henceforth, this series shall be known as Bocchi the Baske.)
I want to say the commentators on page 55 and the spectators on 58 are also a reference to one or both of those manga, but I haven’t read either of them, so I don’t really know for sure. They fit the general sports manga tone, though. Google tells me that 海帝高校 (page 58) is the name of the high school in a comedy manga called 帝一の國, but it’s not a basketball manga.
Page 58 eighth panel, the narration text is calling this chapter 87. Did I miscount somewhere? Or count something as a chapter which wasn’t a chapter?
Page 60 fourth and fifth panels, turns out that having multiple wakaba marks is not illegal. Dunno why I thought it might be. You must display one on the back and one on the front, but beyond that there’s no restriction. You’re even allowed to continue displaying it after the required one-year period, if you still feel inexperienced.
Page 62 fouth panel, Nijika’s use of 備蓄 in her reply suggests this panel might be a reference to the Japanese Government Rice Stockpile - to counter rising rice prices, they basically released the entirety of it onto the markets in 2024-25. Same page fifth panel, Kohoku PA (though the lighting’s not great).
Page 63 seventh panel, Ebina SA, Ebina JCT. Google Maps says Ebina SA is about twenty minutes’ drive from Kohoku PA, but ironically enough, there’s congestion right now as I’m checking it which is adding an extra seventeen minutes to that.
Page 64 first panel, road sign.
Page 65 first panel, this is almost certainly a real product, but… I don’t wanna Google that. Someone else can. 
Page 66 second panel, the record Yoyoko is referring to is the most freshly-baked sweet buns sold in 48 hours. (Is there a different record for savoury buns? For not freshly-baked?) Fourth panel, they cost 380 yen each; three times 380 yen is 1140.