Will's powers, he's learning, don't work the same way El's do (or, at least, the way his friends described El's powers to him). He can't raise his hand and just make things happen in the physical world, but what he can do is scrunch his face up at Dipper for a moment, then pick up a stick of his own to copy Dipper's notes onto a patch of dry sand that is less likely to be erased by a wave.

And then he sways a little on his feet, though that might be less due to the strain of using his powers and more due to the fact that his discharge instructions were to rest as much as possible under the care of his mom, not roam around a new world.