Is there actually anything special about any shave cream / gel, IMO you may as well just use a small amount of liquid soap / hand wash as all you need to do is provide some lubrication for the blade
They contain emollients and lubricants that are better than soap and water. Water provided some lubrication, but it is not the best. They also contain humectants which hydrate the beard/hair (and the skin a bit). If you shave directly out of a 10 minute hot shower, the beard is fully hydrated so this is not a big deal. If you are
not right out of a shower, wait 5 minutes after you apply the product before you shave. (Sorry if everyone knows this).
Gel is denser than foam, so provides more lubrication per cm2.