The reason for leveling, besides personal comfort, is that an absorption style fridge needs to be level to work properly. Compressor type fridges are not level dependent. Not many Class B units come with compressor type fridges, usually an after market modification.
To level, I carry 6 blocks made out of 8 x 2. I have only used 4 of the six while camping. The blocks are in sets of three, with one end tapered so that there is a continuous smooth ramp up to the top block. Each block is pinned to the one below by dropping a 1/4 inch bolt through lined up holes. So for a set of three there are just two bolts. About 90% of leveling entails one or two blocks under the front wheel or wheels. We use a bulls eye level.
The bulls eye level is first used inside the fridge (leveling the van to do this). When the fridge is level, then find a spot on the counter or ledge where you can easily read the level and mark the spot. Thereafter, place the level on the marked spot and go from there. After much practice, I can judge where and how many blocks to use. Sometimes, I put one block crosswise, another block as the ramp and run up only part way. The 4 blocks I use travel with the bolts through the holes, so they stay put - most of the time.