I'm assembling figures for my work in Inkscape. I would like to know if there are features I can use to ensure that labels are consistent distances away from images. Consider the red arrows in this cropped screenshot below - how do I make sure that the indicated distances are identical (they actually look pretty close). I can think of a way to do it but it's cumbersome and I hope that there are better features I'm not yet aware of.

You can use align and distribute or snapping to guide lines.

Alignment is based on the object's bounding box, so you may use a "spacer object". Like group each text with a larger, transparent rectangle.
It can also help with snapping, as then you can use snapping of cusp nodes -corners of the rectangles- (texts would need converting to paths otherwise).

To align the labels in a single row, select them all, then click on this in the Align&Distribute dialog (Shift+Ctrl+A):

For the 'relative to' dropdown, select 'first selected'.

To then have even spacing for both of the rows, a quick way is to create a 'spacer object', that you throw away later.
Align the spacer object (a rectangle is quick) to the top of the electrophoresis, then align the grouped and bottom-aligned (see above) labels to the top of the spacer object (same dialog, different buttons - the button right of the mouse cursor).

Use the same spacer object or a duplicate of it for the other row.

You could also use regularly arranged guides or a grid that you can just snap to.

(what a timing, Lazur )

I guess grids or spacer objects are the best way to achieve this in 0.91. Thanks a lot!