Rashbam: This is a proper matter.

Metzudas David: I saw with understanding of the heart.

Rav Sadya Gaon: He should benefit others, and benefit [also himself] to eat and drink.

Rashbam: He should rejoice in his portion in his lifetime, from what he toiled in his lifetime.

R. Avigdor ¹ : This refers to [learning] Torah.

Seforno: It is good to eat and drink only what is necessary, without excess.

Ibn Ezra, Ri Kara: Because it said that man will leave the world empty, like he came (15), I saw that the only good for one who gathers money is to eat, drink and rejoice.

Seforno: This (that man will leave the world empty) proves like it said above.

Rashi: It is to engage in Torah, which is "Lekach Tov" (Mishlei 4:2).

R. Avigdor: This is making a meal when finishing Torah, like I explained above (refer to 2:24:3:1).

Seforno: It is perfection for eternal life.

Metzudas David: It is to do Tzedakah and Chesed.

Seforno: Even though he toils much for this, all his toil should be for this purpose (perfection for eternal life).

Metzudas David: With all the wealth that he gathered under the sun.

R. Avigdor: His days are short and numbered, and ¹ to bring him to the world to come. "Chayav" is written lacking a Yud, to hint to the 10 days between Rosh Hashanah and Yom Kipur, during which man's income is decreed ² . Therefore, we offer 10 Korbanos [for Musaf of] Rosh Hashanah.

Seforno: The days of this world are numbered and few, and there is much work [to do in them].

Metzudas David: So he should do with all the days that Hashem keeps him alive.

Rashi: He should not gather great wealth, rather, rejoice in the portion given to him.

Rashbam: This is his portion; there is nothing better than it. This is like it says above "Ein Tov ba'Adam she'Yochal v'Shasah?" (2:24)

Metzudas David: All the wealth is the portion that Hashem gave to him. It is proper that he benefit from it, and do with it Tzedakah and Chesed.