Alleviating symptoms

The many, non specific, symptoms of Chronic Renal Failure are caused by the nitrogenous wastes (uraemic toxins) that accumulate in the blood due to renal dysfunction. This syndrome is also called azotaemia.

Since these wastes come from the degradation of proteins, it makes sense to decrease protein intake. This really is efficient and many commercial formulations of  "specific renal diets" are available at your veterinarian clinic.

Nevertheless we should be cautious so as not to decrease protein intake too much since dogs and even more so cats are carnivorous and need to feed normally when they suffer from CRF.
Some substances (AST 120, Chitosan) are interesting alternatives or complements. They bind some uraemic toxins in the gut and help the pet feel better.