Ahhh, that Suzu/Daisy song should be "LoFi - River Background".
As for the Yukari drinking game one.. well, depending which stage of getting closer you mean, it could be either "Formalin Fetus" (when MC asks her that question for 6 shots), or "Purrple Cat - Wild Strawberry" (when Yukari suggests an experiment in the name of science). I assume it's the latter, though, from what you said.
No worries. Enjoy the great songs by those talented artists! :)