When Gilligan goes to write "FREE" on his lemonade sign, There is a faint "F" already on the board, maybe from an earlier failed take or a direction for him to start writing.
Near the end of the dream sequence, when Gilligan makes off with the goose that lays the oranges, the same goose is used for both Bob and his son Patrick, which explains why it goes from being easily held near Bob's chest, but has Patrick running with the goose blocking his view.
The Professor reads that Sodium Chloride is good for planting seeds. That is salt which is well known to kill plants.
It takes a minimum of eight years for an orange tree to bear fruit after planting a seed (in ideal conditions, and as the Professor pointed out, the island's soil was not ideal).
The Professor says that the main problem is lack of Vitamin C. When Gilligan is telling Mary Ann and Ginger about their lack of vitamins, there is a pineapple sitting on the table. Pineapples have more than the minimum RDA of Vitamin C.
The Professor first says that everyone is going to die in just a matter of weeks, and then says planting and growing their own Orange trees will save them. It takes months for an Orange tree to produce fruit.
During the dream sequence, Ginger's theme is played when Jim Backus as Lester J Frothingham III comes on screen.