Bequest" is a will, but not the kind with houses and money. The speaker hands out gifts that no one could really own: a noon he has invented, the sun as a dinner guest, the sea put to work for an apothecary. The title leads us to expect something solemn, and the poem quietly plays with that expectation by giving away things that are impossible to give.
The last line turns inward. The sea becomes "my velvet coat," as if the speaker has wrapped himself in it, and it is hard to tell whether he is giving the sea away or keeping it close. That slippery logic is part of the charm. The speaker seems playful and generous, perhaps a little wistful, since a bequest is usually made when someone is thinking about leaving. The mood is light and dreamlike, but there is a soft undertone of farewell. Judging by the imagery, he treats the whole world as something to be enjoyed, borrowed and passed on with a smile.