The whole question is whether you are ready to immediately jump into a marathon in a minibus right after the plane/train? This time, the minibus will evolve and be faster. But you will still have to travel for about 7 hours.

where should we buy things for fun during the minibus ride?

There might be problems with this. Alcohol is not sold before 9 am in Novosibirsk. It would be more logical to immediately express your gastronomic wishes to Alexey so that he can buy everything at the Lenta store near his house.