A lot of cultural values can be seen in the characters of the Widow Douglas and Miss Watson. The Widow Douglas takes Huck in "and allowed she would sivilize" Huck. That included a series of things, including dressing him nicely, teaching him table manners, teaching him how to read and write, and teaching him about religion and the bible. All of these things are cultural values that are imposed onto Huck. He doesn't take nicely to any of them. Of the decent clothing, he says,"I couldn't do nothing but sweat and sweat, and feel all cramped up." Of table manners he states,
"when you got to the table you couldn't go right to eating, but you had to wait for the widow to tuck down her head and grumble a little over the victuals."
Of the bible, he states of Moses, "I don't take no stock in dead people," and of learning to write and read he says, "I couldn't stood it much longer." Then of heaven and hell he outright states of hell, "I wished I was there," and of praying he feels,
"I couldn't see no advantage about it-except for the other people; so at last I reckoned I wouldn't worry about it any more, but just let it go."
So, all of these things are cultural values that the widow and Miss Watson try to acclimate Huck too, but he doesn't really take nicely to any of them.
The other large cultural value that is seen in the book is people's attitudes towards slavery. They all thought that slavery was good, that runaway slaves were bad, and that to help was runaway slave was "low-down and ornery". Huck reflects that attitude throughout most of the novel; he gets mad at Jim for wanting to buy his children and wife freedom, he promises to help Jim escape but feels dirty about it, he almost tells on Jim several times, and feels as if Providence (or God ) is punishing him for helping Jim on several occasions. So that is another cultural value that is reflected in the novel.
I hope those examples help get you started. Good luck!