To drink with the bistecca that you also bought in the "Clothing" section. Must be Lady Gaga's store!
It's plural. "Noi" is "we", a plural pronoun, and "compriamo" is the form of the Italian verb "comprare" that goes with "noi".
("Compriamo" is "we buy", that is, it's in the present tense, of course. If we wanted to say "we bought" the verb would be different.)
The "noi" can be left out and everyone would still know from the verb alone who is doing the buying.
SINGULAR (I, you, he/she/it)
PLURAL (we, you, they)