The Religious Stuff
As per Leviticus 23:40, during the holiday of Succos (this year October 5-11), Jews are commanded to take one date palm, two willow branches, three myrtle branches, and one citron, and shake them around several times in each of the six directions, once daily, for the seven days of the festival. Jewish tradition mandates that the former three species be tied together in a very specific way, with the citron left on its own and held by the other hand. Severely oversimplified, but should suffice for this question. Relevant Wikipedia page
For the purposes of protecting and transporting these species, the common practice (at least in my community) is that the first three species (which, again, are tied together) are kept in a bag, usually made from plastic, fabric, or velvet with a zipper, or else a long, hard plastic case, with two pieces that snap together (no metal pieces); the citron is typically housed either in a wooden box or a cardboard one with some sort of foam cushioning it.
Given these species and packaging, what travel restrictions should I be aware of to transport these without checking them from the United States to Israel? Are there federal regulations (on either end) regarding such baggage, and does it vary from airline to airline?