You can buy food and drinks on board. Here‘s the menu:
https://www.lufthansa.com/content/da...08_Singles.pdf
You don‘t have to wear a mask at the airport, just on board of public transportation. On board trains (including the shuttle train between T2 and the satellite terminal) a FFP2 mask is mandatory, although I‘ve seen plenty of folks with just a surgical mask in the shuttle at MUC. Same goes for busses, including in case of bus boarding. On board a LH plane you need a FFP2 or surgical mask.