Feasting and rejoicing

Some have the custom to eat a festive meal on the eve of Lag B'omer as well. (Lag B'omer 5751; Hisvaaduyos p. 215) This is in addition to the festive meal that is held during the actual day of Lag B'omer. (Parshas Emor 5750; Hisvaaduyos p. 176)

The Alter Rebbe states in his Shulchan Aruch (Orach Chayim 493:5), that "We have a custom to somewhat increase in joy on this day. In Igros Kodesh (p. 117), he states, "…on the 18th of Iyar, they rejoice and exult in Hashem with all heart and soul, and hold a day of feasting and rejoicing." (Parshas Acharei-Kedoshim 5750, fn. 92; Hisvaaduyos p. 148)