If you're a reader and like to read while on vacation, plan on having some time to do this. A deck of cards, checkers, or a backgammon set can be fun to have around in the evenings. Certainly during the trip they can help break up the monotony of driving. Swimming stuff, including suits and towels. I like to have a pair of water socks, too.
Some people love 'em, some people hate 'em.
Take 'em if you love 'em. I suspect the hotel room towels are probably pretty plush. Air travelers are loathe to take up precious packing space on big fluffy towels. Also, those who don't like water sandals should take a pair of cheap flip flops. A travel alarm clock.