Sealine we have had one for about ten years. Use it for scuba to keep towels and shirts dry. They are quite durable think getting thrown on and off a boat over 200 times, no leaks as of last usage.
A 40 liter bag will hold beach towels, shorts, hats, Tshirts, glasses for two, but it is on the big side.
I have some of the much smaller, ~5L, Sealine bags for keeping things dry in the kayak on overnight trips. They were on the shelf at REI so that's what I got. Work great.
I have a 13L Sea to Summit Big River I like a lot. It's fairly thick material that seems fairly tear resistant which was important to me since I was replacing a dry bag I tore on a sharp rock. The only thing I didn't like is that it didn't come with a carrying strap. I used the one off of the torn one though so that wasn't an issue.