As Meags said, bluebottles, yes! Jellyfish, too - like someone dumped out lots of little tubs of clear Jell-O randomly at the high-tide mark.

Seaweed (the thick and wavy, coarse-surfaced kind and the ones with the 'bulbs' all along it), rocks all washed clean. Also the ones that look like really long, dark-green grass. And seashells - the little fan-shaped ones in brown and cream, the small black ones from the sea snails that cling to the rocks at high tide, and I remember finding purple coral-like ones at certain beaches - although I haven't seen them in years. Cuttlefish bones (good for taking back for the budgie cage) and shell-sand mixed in among the grit-sand at the rocks.

A lot of it depends on the kind of beach and the weather, too.