The minhag is to have a little more food and drink on the day following Pesach. [1]
The minhag is not to fast on any Issru Chag, the day following a Yom Tov. [2]
References
↑Rama 429:2 based on Sukkot 45b, see Maharil who explains that the reason for this is that the Korban Shlalmim of the holiday is eaten for 2 days and so it can be eaten even on the day after the holiday.
