2. Question: Why can you have a snack before fulfilling the mitzvah of lulav and esrog if it’s delayed coming to you but if you are going to a later minyan to hear megilla you should not even snack until after you hear megilla?
A. The fast of Taanis Esther ends at nightfall but you shouldn’t eat anything until after you fulfill the mitzvah (of megilla) just as you shouldn’t eat anything until after you fulfill any other mitzvah like lulav or shofar etc.
B. There is more of a mitzvah to fulfill the megilla reading in a congregation in order to publicize the miracle.
Answer: You can taste before lulav and esrog if there is a delay because it’s a mitzvah you do by yourself. But megilla should be read in a group and we are concerned even if you eat a snack you might miss the mitzvah all together or at least the start of the reading, which means you’d have to hear it again by yourself not in a group. (Dirshu Mishna Berura back page 131 footnote 32)