137:5 One is forbidden to eat before waving the lulav. If one is traveling and expects to come to a place where there is a lulav and esrog – and also those living in the outskirts who are having a lulav and esrog sent to them – must wait up to (but not including – Shaar HaTziyon 652:6) midday but no longer, because it is forbidden to fast beyond this point on yom tov or chol hamoed. If one would feel faint if he waited until midday, he may eat something sooner. However, one who does not feel faint should be stringent even when it comes to eating just a little.
137:6 It is permitted to replace the lulav into its water on yom tov; one may even add water, but he may not change the water. On chol hamoed, it is a mitzvah to change the water so that the lulav will remain fresh and nice. The practice is to take new aravos on each day of chol hamoed. This is considered an enhancement of the mitzvah.