The 3D features are less than oversophisticated.
In any case (depending on version and options), it is worth considering the suitable tools and ways for each part of the artwork.
You may see it as:
A) A normal (unrotated) artwork consisting of the contents not touching the inside of the bottle, which is just as it would be out there;
B) The parts of the sand and water that touch the inside of the bottle and follows;
C) The (inner and outer) shape(s) of the bottle, partly transparent, covering A) and B),
and you can create each independently.
A) can be made as you would in any other case.
B) can be made in different ways, depending on version and options; judging by the drawing, the rounded appearance of the bottom parts may be created with simple means (including (expanded) blends, each based on objects with a straight horizontal top segment, the top of then cut off or masked out to fit the actual top shape, and gradient meshes).
C) can be made using 3D, or in other ways (such as blends and gradient meshes).
To supplement Jacob's great answer, you might check out this tutorial:
It seems to me that you will be able to apply the techniques in this tutorial to your project. Good luck!
Do you know if there's an easy way to create half of a 3D bottle? I know that you can do a effect - revolve after you just draw the outline of one side, but am wondering if you can just revolve 180 degrees instead of the full 360 somehow. If I could do that, then I could align the two halves and put all my content in between them. Right now I'm just using two filled (flat) outlines of a bottle with a little gradient on the top and bottom to make them look round, but it would be really nice if they were more 3D looking.
Do you know if there's an easy way to create half of a 3D bottle?
That should be obvious: There's a setting in the 3D Effect Revolve dialog for how many degees to sweep the base path.
The problem is, you are simply using the wrong tool. You are trying to do with Illustrator's very limited 3D Effect things that it can't really do.
3D Effect does simple linear extrusion and lathe (revolve), and that's all. It can't do pipeline extrusions. It can't perform boolean operations (add, subtract, intersect) on its resulting 3D objects (only on the initial paths that you are extruding or lathing). It can't even have its two different kinds of 3D objects (an extrusion and a revolve) residing in the same coordinate space (i.e.; in the same model). So you have to resort to faking such things by creating separate objects, each with its own coordinate space, and just stacking their rendered 2D results on the page.
In other words, it can't build 3D objects actually shaped like the sand, water, etc. in your bottle. If you start with an irregular shape defining the side profile of the sand surface and extrude that in a direction across the width of the bottle, 3D Effect cannot then "trim away" the rounded bottom of that object to make it conform to the interior surface of the bottle.
If you try that the other way, by drawing the cross-section of the sand and then extruding it longitudinally along the length of the bottle, it's conceivable that you could draw a Bevel profile to reasonably correspond to the interior curvature of the bottle. But that bevel would be applied to all edges of the cross-section, not just its "bottom."
The proper way to use 3D Effect for this kind of project is to just use 3D Effec to draw and position the geometry of the bottle and/or map artwork to the resulting surfaces. Then use the regular 2D drawing tools to actually finish the drawing of the contents. Or (and better), just use 3D Effect as a "rough out tool" to establish the main geometry, and then use the results as a temporary "sketch" over which you draw the whole rendering as 2D artwork.
If you insist on actually building this as a 3D model, you should be using a proper 3D modeling/rendering program, not Illustrator's 3D Effect. 3D Effect is implemented for simple extrusion and lathing of simple 2D shapes, not for building whole scenes of different kinds of 3D objects.
Continuing your attempt at this using nothing but 3D Effect is folly. It will not yield anything approaching the quality of doing it in a proper 3D modeling/rendering program, and will take much more time and effort.