In the final showdown, Trace Adkins fires more than 20 shots from a pump action shotgun without ever reloading. The final point where he could have conceivably reloaded is followed by eleven rapid fire blasts.
Captain Wally's Walkie Talkie ended up in the girl's sleeping area on the island; when in the previous scene Captain Wally dropped it in the reef and swam after it and was eaten by the Great White.
When Harlan arrives on the island, Jessie tells him there were "7 of us". There were 8: Will, Sunny, Brianna, Ty, Emma, Jessie, Wally and Beth.
At about 1:13 and on, when Harlan uncorks his bottle there is a windsurfer in the background just outside of the reef.