Definitely bring a good hiking bag. I had a Kal Gav I bought for about 135 shekel; I think it was 55 liters.
Lots of girls from Seminary were doing Yam Liyam when I was. They all did really well; except they underpacked food so I was feeding them the whole time. Undereating when on a strenuous hike is no way to lose weight…
And a towel is probably a good idea too
Anybody going should be sure they know how to read a map or they should get a tourguide