An offering of barley in prescribed for Pesah (Passover), whereas on Shabu'oth, an offering of wheat is brought. Barley is what we feed to animals, whereas wheat is food for humans. From this we can understand that Pesah symbolizes our physical freedom, inasmuch as our bodies share certain aspects in common with animals. Shabu'oth, on the other hand, represents our spiritual redemption, which was the stage we reached when we received the Torah.
It says in the Shulhan 'Arukh that one will not see any sign of blessing if one does work on 'Ereb Shabbath, from the time of Minha. There are those who are of the opinion that this refers to the earlier time of Minha Gedolah, whereas others opine that it is the later time of Minha Qetanah (nine and a half hours into the day). The Ben Ish Hai states that it is the later time (See http://www.atorahminute.com/2012-09-14 ). One should apply the same rule to Yom Tob also. Obviously, this does not apply to work that is needed to be done for the Holiday itself.
On 'Ereb Sukkoth (during the day prior to the start of Sukkoth), one should not eat a full meal after midday, since the Torah commands us to eat at night, and we should do so with a hearty appetite. Even though the requirement to eat a Kezayith (1 oz) of bread on Shabu'oth is not DeOraitha (a Torah obligation), nevertheless, it is appropriate to do so before any Yom Tob. This applies to a meal, but snacks are permitted.
(See Shulhan 'Arukh with Rama, 251:1. Ben Ish Hai, 2nd year, Parashath Lekh Lekha, Oth 20, 1st year, Haazinu, Oth 3. Hilkhoth Haggim, Maamar Mordekhai [Eliyahu], 21:6-8)
Shabu'oth, Shabuot, Shavuot, Shvuos,