Seeking Alternative Food/Treats

My cat just started today on Waltham's Renal Support
(semi-moist) and my vet said to feed her one 3 oz. pouch
daily and her water. This will hopefully bring down her
BUN and phosphorus levels. In 6 weeks she goes back for
another blood test. She is nearly 18 and I assume my vet
plans to keep her on this diet for the rest of her life.
Apparently my vet feels she can survive on just 3 ounces
of food a day (she is 4 1/2 pounds and the pouch says 1
daily at her weight).
My question is does anyone know of anything else I can
feed her that does not contain protein or phosphorus?
I agree with my vet, but I'd like to be able to feed her
something else occasionally that won't bring up her levels.
If you think I should not seek safe alternatives and strictly
follow my vet's advice, let me know that too.

Your cat is 18 and only 4 and 1/2 pounds??

I'm not sure maybe someone else can help you. If the pouch says its ok and the vet says its ok... I guess its ok?

bryan your vet would be the best one to ask, as he is aware of the cat and sees the condition of the cat- etc...18 is a good long life, you are to be commended for taking such great care of your cat, though I admit the low weight has me concerned a bit. Has the cat been ill a very long time?

She started showing signs of a problem just 2 weeks
ago. She was crying a lot so I took her to the vet
last weekend. Now she is on Waltham's semi-moist
(3 oz. pouch) but seems to want more food - that is
why I'm searching for a safe alternative to supplement
her diet. Tomorrow I will call my vet to get his opinion.