Treats for PU cat?

About 3 months ago my 2 yr. old male cat had PU surgery (after repeated struvite (sp) crystal blockages). Since then he's been on Royal Canine SO. I was wondering what I could give him now and then as a treat that would be "safe" (not causing crystal formation) I know he's not likely to block (but that it can happen). I just can't take any chances right now as the last vet bills pretty much wiped out our savings. I know this isn't a major thing (even though he thinks it is) but, any advice is appreciated. Thank you.

since your kitty is on a RX the best one to ask about " safe" treats is your vet ... many use the dry food as a treat

Coco was on that same food and had struvite crystals and stones.
I was told there were no treats she could have.

Yeah, I do give him a little of the dry as a treat, I was just hoping there was something else to give him a little variety. Thank you.