Continuity mistake: When Tom Hanks is in the dinghy by himself, the outboard motor has no cover. He falls into the water and the dinghy circles him several times. One of the shots shows the motor with its cover in place. (It is an Evinrude motor).
Visible crew/equipment: When Madison enters Bloomingdales, you can see the reflection of Ron Howard in one of the mirrors.
Revealing mistake: The saleslady in Bloomingdales tells Madison she shouldn't be wearing boxer shorts, however, when doing the exercises in front of the TVs, she bends over a few times and the lines show panties, not boxer short lines.
Continuity mistake: At the beach, Walter and one of the twins carry a box and are inches away from the boat. Half a second later, when the angle cuts to Allen asking the other twin, the first couple is standing behind, far from the boat, holding the same box and repeating the previous movements.