I have bouillion cubes occasionally.
The ones I use are called "just bouillion" and I get them from Sainsburys. The cubes are quite big so I have 1/3rd of a cube at a time, sometimes with some dried minced garlic or herbs in, made up with boiling water to about 1/2 to 2/3 of a mugful. Works out at about 16 cals iirc, with some carbs but quite a lot of fat.
I don't drink tea or coffee so I enjoy having something hot for a change sometimes! This is maybe once or twice a month though so not a very regular thing.