Alternatives to salt and vinegar crisps

FiL blocks any change, whatever it is. He has, we think, kidney disease and congestive heart failure, and has been told to severely reduce his fluid intake as he has so much edema. His eating is poor, and he has been surviving on toast and marmite and bags of crisps presumably this is the change in taste kicking in now.....I would prefer him to have developed the sweet tooth many have, but he is all for strong and salty.

Obviously this is really bad for his heart/kidneys but we're not getting anywhere with substituting something slightly healthier....he'll try it for a couple of weeks then revert back (and we've not got him on kale and quinoa either!) I think I know the answer is that there probably is no answer......at least he's happy even if it increases the chance of a speedy return to hospital. My husband is agonising over 'enabling' him by supplying what he wants, but I think he just won't eat anything if we stop getting them. Im very nutrition conscious but I may be beaten on this......any suggestions anyone? And are we doing the right thing by letting FiL call the shots, rather than force the issue? I feel he needs much more carer time, or even CH but he has capacity, he's just a stubborn old codger who's getting even worse!