ou'll have to remember that if your PKD kidneys are rather large, they will press upon other organs including your stomach and bowels. It's not necessarily the food but sometimes the amount of food, however you'll likely find that more acidic foods or foods high in sugar will be harder to digest or deal with.
As far as a food that helps I don't believe there is a magic bullet. You have to eat right and hydrate properly if you're allowed to. If your renal function is good and you haven't been told to restrict anything, then living a healthy and active life is the way to go. Make sure you drink plenty of water because PKD kidneys tend to let fluid pass right through them.
If your kidney function is compromised to the point of being told to restrict certain things like potassium or phosphorus then you need to be referred to a renal dietician. At this point, you should check with your nephrologist and dietician before making changes.

I complained for 5 years to my nephrologist about various ailments associated with PKD. It wasn't until I went to the Mayo Clinic in October 08 that I found out that I should be limiting my protein in take. I was slightly anemic YET my iron levels were very high. They said "too much protein". Just for reference my creatinine is .9, so not bad yet. I'm limiting my protein now to around 40 grams per day and eat small portions at each meal. EVERYone diagnosed with PKD should limit protein intake as it is hard for our bodies to process. Animal protein is the hardest to digest...so, about 2 ounces at each meal is what I try to follow. It's HARD but I feel MUCH better when I eat this way. There is protein in almost EVERYthing. Even most vegetables. It's been a hard transition. But since there is no cure, I'm trying to slow the progression as much as possible.

Foods I avoid, or limit: bagels, pasta, breads...blow up in my stomach. tomatoes don't bother me. high fatty foods: avoid at all costs.

I find that if I eat very small portions throughout the day, then things run smoothly...but I do have a tendency to not eat breakfast, then by mid-morning I'm starving, and I usually then eat half a bagel, or toast.

Instead of eating off a regular plate, I eat off a teacup saucer, or very small plate! This way I limit my portion! Here in the US, restaurants typically pile tons of food on your plate...I can feed my family from it!

And of course, drink plenty, plenty of water...I only drink water...and wine! I won't give up my glass (or two) of wine! No beer (anymore) or carbonated drinks...my belly can't handle it!