folding hot shoe spirit level

[Willie]

On the 35mm and 120 cameras I use the hot shoe level, the model that flips up and like it.
For the 5x7 and 8x10 I use either a torpedo level or this solar powered calculator/level/angle finder/tape measure. It is small and the tape measure helps with bellows extension for figuring exposure.
Have tried the small block/cube type levels and they work but I like the flip up as it stays on the smaller cameras.

[Kerosene Hat]

I've done well with a bag of 20 small levels for $8 from Amazon / China, and affixing a couple to my field camera with industrial strength Velcro. A non-fastened one helps me get my front standard level. YMMV