In Gittin 56b there is a conversation between Vespasian and R' Yochanan ben Zakkai. Vespasian offers to grant a wish of R' Yochanan's
אלא בעי מינאי מידי דאתן לך
R' Yochanan proceeds to ask for 3 things
אמר ליה תן לי יבנה וחכמיה ושושילתא דרבן גמליאל ואסוותא דמסיין ליה לרבי צדוק
How did R' Yochanan know he could ask for more than 1 thing and why did he stop at 3? I am aware that the gemarah discusses why he didn't ask to abandon the siege, but he could have asked for many other things.