Should I Daven Hallel with the Minyan if I have no Lulav?
The recitation of Hallel on Yom Tov and Rosh Chodesh was instituted primarily within the context of a minyan (prayer quorum [of at least ten men]). On Sukkos, the na’anuim (“movements,” i.e. the shaking in all directions) of arba’as haminim (the Four Kinds) during Hallel are regarded as a primary aspect of the mitzvah of lulav (though the mitzvah is fulfilled in a basic way without them). This leads a person who does not own a set of arba minim to make a difficult choice: should he daven Hallel with the minyan without being able to practice the na’anuim during Hallel—or should he daven Hallel later b’yechidus (privately) with a borrowed* set of arba minim?
There is no clear answer to this conundrum. There are poskim who maintain that it is better to recite Hallel at a later time to be able to fulfill the mitzvah of lulav optimally, while others support a lulav-less but minyan-enabled Hallel. The rule in such a case is: “D’avid k’mar avid, d’avid k’mar avid” (one who does like this has acted [legitimately] and one who does like that has acted [legitimately])— so ha’bocher yivchar (the chooser should choose).
The optimal solution for a person without a lulav is to borrow* the arba minim from a neighboring davener who has completed the na’anuim—even if only to do the actual na’anuim as he recites the relevant phrases in Hallel—and then quickly catch up with the minyan.
*When borrowing a set of arba’as haminim from another to perform the mitzvah on the first day of Sukkos (and outside Eretz Yisroel, on the second day, too), it must be matanah al menas l’hachzir (a gift on condition of returning it)—see Halachah #725 for details. It is recommended to be careful when borrowing for Hallel, too; it is questionable whether the na’anuim—as an important feature of the mitzvah of lulav—is properly fulfilled if using an improperly borrowed set.